Research Interests:
Research Interests:
Research Interests:
Rice husk is an agro waste that is not used in valuable ways especially in Sri Lanka other than as an alternative energy source. The conventionally burnt rice husk contains about 80-90% silica. Thus, these rice husk ash (RHA) could be a... more
Rice husk is an agro waste that is not used in valuable ways especially in Sri Lanka other than as an alternative energy source. The conventionally burnt rice husk contains about 80-90% silica. Thus, these rice husk ash (RHA) could be a good replacement for commercially used silica filler in non-marking tread compounds. This study dedicated to research on possibility of using RHA and amorphous silica extracted from RHA as filler in non-marking tread compounds. The ash color RHA was obtained from conventionally burnt of rice husk at high temperature (550 C-700 C). The sodium silicate slurry was obtained by dissolving RHA in sodium hydroxide, heated above 140° C and stirred for 4 hrs. The slurry was filtered and filtrate was used to produce silica gel using sulphuric acid. This reaction was taken place at temperature 80° C-90° C range. The addition of sulphuric acid was done very slowly until medium become acidic. This was observed by using litmus papers. Then gel was allowed to age...
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Free fluoride ions and the metal complexes of fluoride ions significantly affect the quality of drinking water. It shows both beneficial and detrimental effects to the human health. Several techniques based on Ion Selective Electrode... more
Free fluoride ions and the metal complexes of fluoride ions significantly affect the quality of drinking water. It shows both beneficial and detrimental effects to the human health. Several techniques based on Ion Selective Electrode (ISE), ion chromatography and colorimetry has been developed to assess the fluoride levels in drinking water. However, all those above methods require sophisticated instruments, which must be operated inside laboratories. The objective of this project is to develop a fluoride sensitive strip that is cost effective and can be used in the field. The SPADNS method is a well-accepted method for fluoride analysis. Reference to this method, the fluoride sensitive strip is designed. Whatman 41 ashless filter paper was modified with titanium butoxide via a sol-gel process. The red color SPADNS-Zr dye was grafted on to the titania layer of the modified strip. The resultant dye sensitized strip is dark blue. The modified strip shows rapid and obvious color change...
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Research Interests:
Flooring products with rubber matrices is a smr Il, but growing sector in the world floor coverings market. Both plastic and rubber floor covering p oducts are not widely used in Sri Lanka. Such flooring includes mats, rolls, sheets, and... more
Flooring products with rubber matrices is a smr Il, but growing sector in the world floor coverings market. Both plastic and rubber floor covering p oducts are not widely used in Sri Lanka. Such flooring includes mats, rolls, sheets, and indoor ant l outdoor tiles. Among the materials for flooring, natural rubber blended with synthetic rubber is one of the cheapest ingredients especially for countries like Sri Lanka since the availability of natural rubber for considerably low cost. The pristine natural rubber and its blends with synthetic rubber normally show retarded mechanical properties. Thus, reinforcement with fillers and vulcanization is commonly practiced technique to enhance the mechanical characteristics. The aim of this work is to develop and evaluate the mechanical properties of rubber composites reinforced with tyre waste (crumb rubber) and amorphous silica extracted from rice husk. For this study, two different sizes of crumb rubber particles of average size less than ...
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Research Interests:
Agro-industrial waste has become a major environmental issue in most parts of the world. Rice husk is one of the major agricultural wastes especially in Asian countries. It is currently thrown away into landfills or rarely use as an... more
Agro-industrial waste has become a major environmental issue in most parts of the world. Rice husk is one of the major agricultural wastes especially in Asian countries. It is currently thrown away into landfills or rarely use as an alternative energy source, which in turn produce another waste, rice husk ash (RHA). Silica is the major component in well-burnt RHA. This work was aimed to evaluate the feasibility of utilizing silica extracted from RHA and another industrial waste, used tyre treads, with natural rubber to develop composite with enhanced mechanical properties especially for flooring products such as rugs, pavement blocks, door mats, etc. In this work extracted silica was characterized using Fourier-transform infrared spectroscopy, X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy (SEM). The SEM images confirmed that the extracted silica is in the nanometer to sub-micrometer length scale in size. Further our results confir...
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Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have demonstrated... more
Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have demonstrated potential as intracellular imaging markers, as well as building blocks for light harvesting devices. The current work investigates the structure and stability of poly-dots of di-alkyl para polyphenyleneethynylene (PPE) conjugated polymers in solution and follows their assembly at interfaces. Small angle neutron scattering measurements of the poly-dots in water have shown that at low concentrations, stable unimolecular spherical poly-dots are formed with a polydispersity that corresponds to that of the polymer itself. With increasing concentration, yet, below the critical micelle concentration of these rod-like polymers in good solvents, the size and density of the NPs increases, however the spherical symmetry is retained. The nature and length of t...
Research Interests:
Research Interests:
The self-assembly of a highly incompatible siloxane containing semi-fluorinated diblock copolymer, polytrifluoro propyl methylsiloxane-b-polystyrene (SiF-PS), in toluene, a selective solvent for polystyrene, was studied using Small Angle... more
The self-assembly of a highly incompatible siloxane containing semi-fluorinated diblock copolymer, polytrifluoro propyl methylsiloxane-b-polystyrene (SiF-PS), in toluene, a selective solvent for polystyrene, was studied using Small Angle Neutron Scattering. Incompatibility ...
Research Interests:
Research Interests:
Polythiophene and its derivatives are valuable conjugated polymers due to their physical properties and applications in various fields. Precursors of polythiophenes were conventionally obtained from petrochemical byproducts, which are... more
Polythiophene and its derivatives are valuable conjugated polymers due to their physical properties and applications in various fields. Precursors of polythiophenes were conventionally obtained from petrochemical byproducts, which are non-renewable. Thiophene and its derivatives had been found naturally in Tagetes species such as Tagetes erecta, Tagetes tenuifolia, etc. Tagetes species produce 2, 2’:5’, 2’’-terthienyl (Alpha-T), 5-(3-buten-1-ynyl)-2, 20-bithienyl (BBT), 5-(4-hydroxy-1-butynyl)-2, 20-bithienyl (BBTOH), and 5-(4-acetoxy-1-butynyl)-2, 20-bithienyl (BBTOAc), which are accumulated in different parts, specifically in the roots of the plants. These thiophene derivatives were extracted and identified by GC-MS, Uv-vis, FTIR and TLC analysis. The partially purified plant extract is polymerized through one step oxidative free radical polymerization to obtain polythiophenes. Product characterization has revealed that the selective polymerization of thiophene derivatives results...
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The interfacial behavior of multi block copolymer thin films results from a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the interfaces. Here... more
The interfacial behavior of multi block copolymer thin films results from a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the interfaces. Here in we report a study of thin films of ABCBA penta block copolymers, anionically synthesized, comprising of centered randomly sulfonated polystyrene block to which rubbery
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ABSTRACT The formation of hydrophilic modified disubstituted para-polyphenyleneethylene (PPE) nanoparticles (NP) complexes in aqueous media and their assemblies have been investigated. Both PPEs and gold NPs are electro-optically active.... more
ABSTRACT The formation of hydrophilic modified disubstituted para-polyphenyleneethylene (PPE) nanoparticles (NP) complexes in aqueous media and their assemblies have been investigated. Both PPEs and gold NPs are electro-optically active. Controlling their association would allow formation of electro-optical tunable responsive materials. Small Angle Neutron Scattering (SANS) in conjunction with Atomic Force Microscopy (AFM) has been used to characterize the structures of the complexes formed. SANS studies have shown that spherical core shell NP-P complexes are formed in dilute solutions, with the gold NPs surrounded by almost fully stretched out PPE chains. With increasing the concentration of the NP-PPE complex in solution chains which consist of the basic core-shell aggregated are observed. These NP-PPE complexes were allowed to assemble at a solid surface. While the basic building block, observed by AFM, remains spherical, they assemble in different ways from random 2-d arrays to cable like structures, depending on the interaction of the NP with the PPEs and the nature of the PPE side chains.
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... Madhusudan Tyagi ( NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899). ... Alkyl di-substituted \textit{para-polyphenyleneethylene} (PPE) associates into several complex fluids in... more
... Madhusudan Tyagi ( NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899). ... Alkyl di-substituted \textit{para-polyphenyleneethylene} (PPE) associates into several complex fluids in dilute solutions of toluene. ...
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The permeation and distribution of solvents in polymer nanocomposites is governed by the way the nanoparticles (NP) associate within the matrix polymer. We have previously shown that in thin films interfacial effects affect the... more
The permeation and distribution of solvents in polymer nanocomposites is governed by the way the nanoparticles (NP) associate within the matrix polymer. We have previously shown that in thin films interfacial effects affect the distribution of the NP. The current work focuses on ...
Research Interests:
Solvent affinity drives the association of diblock co-polymers in selective solvents. The shape of the micelles is affected by the size of the blocks and their interaction with the solvent. Most experimental and theoretical studies have... more
Solvent affinity drives the association of diblock co-polymers in selective solvents. The shape of the micelles is affected by the size of the blocks and their interaction with the solvent. Most experimental and theoretical studies have investigated solutions of diblocks ...
Research Interests:
The structure of polymers within nanocomposites is strongly affected by the confinement of the polymer to the interface with the nanoparticles and the method of blending. In nanocomposites of Nylon 6 and clay particles are made by chaotic... more
The structure of polymers within nanocomposites is strongly affected by the confinement of the polymer to the interface with the nanoparticles and the method of blending. In nanocomposites of Nylon 6 and clay particles are made by chaotic blending, the strength of the chaotic ...
Research Interests:
The dispersion and orientation of the nano particles within polymeric matrices determine their properties. They depend on inherent characteristics such as miscibility, entropic barriers, structure of the polymer etc., and on processing... more
The dispersion and orientation of the nano particles within polymeric matrices determine their properties. They depend on inherent characteristics such as miscibility, entropic barriers, structure of the polymer etc., and on processing conditions under which the polymer and the particles are mixed. Chaotic flow patterns have been used to define the structure and orientation on a micron length scale. In efforts to derive quantitative correlations, we carried out structural studies using X-ray, AFM and TEM on Nylon 6/modified clay nano composites as a function of the strength of the chaotic advection in a smart blending process. On the micron length scale, the clay particles are dispersed into multi layers, where the thickness of these sheets and the orientation and the distribution of the clay particles are controlled by the strength of the chaotic advection. On the molecular level, increasing the strength results in increase of the gamma crystal form of the Nylon, a higher internal energy state, in which hydrogen bonds are formed between parallel chains. The structure on the micron level is attributed to the chaotic mixing which o the molecular level it is may be attributed to the fractal nature of the process.
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The assembly of lignin molecules from a variety of sources is followed using small angle neutron scattering. The degree of branching of the lignin molecule, which varies with source, plays a crucial role in determining their association... more
The assembly of lignin molecules from a variety of sources is followed using small angle neutron scattering. The degree of branching of the lignin molecule, which varies with source, plays a crucial role in determining their association behavior.
Research Interests:
Research Interests:
The distribution of Polyhedral Oligomeric Silsesquioxanes (POSS) nanoparticles) in thin films of symmetric diblock copolymer polystyrene-b-poly dimethyl siloxane (PS-b-PDMS) was studied by neutron reflectometry. Blending of nanoparticles... more
The distribution of Polyhedral Oligomeric Silsesquioxanes (POSS) nanoparticles) in thin films of symmetric diblock copolymer polystyrene-b-poly dimethyl siloxane (PS-b-PDMS) was studied by neutron reflectometry. Blending of nanoparticles (NPs) with polymers provide a pathway to tune properties of the polymer such as conductivity, mechanical strength, optical activity as well as dewetting, where the properties depend on the distribution of the NPs. Controlling the distribution of NPs in polymers thin films however, remains a challenge where entropic contributions drive segregation of the NPs to the interface. Different approaches were taken including modifying the interfacial interactions of the NP. The current study investigates effects of the relative size of the NP with respect to that of the polymer layers following distribution of POSS cages which consist of a silicon cage in a symmetric PS-PDMS. The temperature was varied from room temperature to 150^oC, investigating the distr...
The slow dynamic processes in amorphous ionic polymers are affected by physical cross-links resulting from clustering of the ionic groups. Therefore in addition to entanglement barriers, the motion of the polymers is coupled to the... more
The slow dynamic processes in amorphous ionic polymers are affected by physical cross-links resulting from clustering of the ionic groups. Therefore in addition to entanglement barriers, the motion of the polymers is coupled to the dynamics of the ionic clusters where the resulting dynamics is an interplay between the effects of the two types of barriers. Using neutron reflectometry we have probed a model system where interfacial diffusion of a Van der Waals polymer, polystyrene, into its sulfonated analogs. Results controlling the molecular weights that determine the overall number of entanglements as well as the degree of sulfonation which affects the strength and number of the ionic clusters will be presented. Comparison to the diffusion of polystyrene into polystyrene will resolve the effects of the ionic clusters from those of entanglements. The presence of the physical cross-links slows down the dynamics significantly with respect to that of polystyrene and an asymmetric proce...
ABSTRACT The mechanical, thermal and rheological properties of polymers can be improved by embedding organic nanoparticles (NPs). However, controlling the dispersion of NPs is often challenging due to thermodynamic and kinetic... more
ABSTRACT The mechanical, thermal and rheological properties of polymers can be improved by embedding organic nanoparticles (NPs). However, controlling the dispersion of NPs is often challenging due to thermodynamic and kinetic incompatibilities between particles and matrices. The current work focuses on the dispersion of chemically identical NPs in a polystyrene matrix. These NPs were made through a micro-emulsion technique using styrene and divinylbenzene (DVB) monomers. Polystyrene nanoparticles with controlled interfacial roughness and targeted styrene densities were achieved by controlling DVB volume fraction during synthesis. The dispersion of these NPs in deuterated polystyrene matrices was followed by Small Angle Neutron Scattering as a function of NP concentration and matrix molecular weight. At low NP concentrations, individual NPs are well distributed in the matrix, while aggregates were formed at higher concentrations in high molecular weight polymer matrices. Shape of the aggregates as well as the minimum concentration of NPs required to form aggregates were affected by the surface roughness and softness of the NPs.
Research Interests:
Self-assembly of block copolymers in selective solvents was used to form a nanoparticle (NP)/polymer hybrid micelles. These micelles can be used as a cargo vehicle for other substances such as drug delivery, and as building blocks for... more
Self-assembly of block copolymers in selective solvents was used to form a nanoparticle (NP)/polymer hybrid micelles. These micelles can be used as a cargo vehicle for other substances such as drug delivery, and as building blocks for polymer-nanocomposites with controlled ...
We use neutron reflectivity to study the effects of harsh environments on the composition and structure of Ta2N films. We investigated samples with a 700 Å Ta2N layer, annealed in vacuum, hydrogen, and air, in an attempt to simulate the... more
We use neutron reflectivity to study the effects of harsh environments on the composition and structure of Ta2N films. We investigated samples with a 700 Å Ta2N layer, annealed in vacuum, hydrogen, and air, in an attempt to simulate the effects of aging on Ta2N thin ...
Research Interests:
The dispersion and orientation of the nano particles within polymeric matrices determine their properties. They depend on inherent characteristics such as miscibility, entropic barriers, structure of the polymer etc., and on processing... more
The dispersion and orientation of the nano particles within polymeric matrices determine their properties. They depend on inherent characteristics such as miscibility, entropic barriers, structure of the polymer etc., and on processing conditions under which the polymer and the particles are mixed. Chaotic flow patterns have been used to define the structure and orientation on a micron length scale. In efforts to derive quantitative correlations, we carried out structural studies using X-ray, AFM and TEM on Nylon 6/modified clay nano composites as a function of the strength of the chaotic advection in a smart blending process. On the micron length scale, the clay particles are dispersed into multi layers, where the thickness of these sheets and the orientation and the distribution of the clay particles are controlled by the strength of the chaotic advection. On the molecular level, increasing the strength results in increase of the gamma crystal form of the Nylon, a higher internal ...
Research Interests:
The interaction of beta-cyclodextrin (beta-CD) with mixed bilayers composed of sphingomylein and cholesterol (Chol) above and below the accepted stable complexation ratio (67:33) was investigated. Membranes with the same (symmetric) and... more
The interaction of beta-cyclodextrin (beta-CD) with mixed bilayers composed of sphingomylein and cholesterol (Chol) above and below the accepted stable complexation ratio (67:33) was investigated. Membranes with the same (symmetric) and different (asymmetric) compositions in their inner and outer leaflets were deposited at surface pressures of 20, 30, and 40 mN/m at the solid-liquid interface. Using neutron reflectometry, membranes of various global molar ratios (defined as the sum of the molar ratios of the inner and outer leaflets), were characterized before and after beta-CD was added to the subphase. The structure of bilayers with global molar ratios at or above the stable complexation ratio was unchanged by beta-CD, indicating that beta-CD is unable to remove sphingomyelin or complexed Chol. However, beta-CD removed all uncomplexed Chol from bilayers composed of global molar ratios below the stable complexation ratio. The removal of Chol by beta-CD was independent of the initial structure of the membranes as deposited, suggesting that asymmetric membranes homogenize by the exchange of molecules between leaflets. The interaction of beta-CD with the aforementioned membranes was independent of the deposition surface pressure except for a symmetric 50:50 membrane deposited at 40 mN/m. The scattering from 50:50 bilayers with higher packing densities (deposited at 40 mN/m) was unaffected by beta-CD, suggesting that the removal of Chol can depend on both the composition and packing density of the membrane.
Research Interests:
ABSTRACT Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have... more
ABSTRACT Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have demonstrated potential as intracellular imaging markers, as well as building blocks for light harvesting devices. The current work investigates the structure and stability of poly-dots of di-alkyl para polyphenyleneethynylene (PPE) conjugated polymers in solution and follows their assembly at interfaces. Small angle neutron scattering measurements of the poly-dots in water have shown that at low concentrations, stable unimolecular spherical poly-dots are formed with a polydispersity that corresponds to that of the polymer itself. With increasing concentration, yet, below the critical micelle concentration of these rod-like polymers in good solvents, the size and density of the NPs increases, however the spherical symmetry is retained. The nature and length of the substituents affect the internal density and the degree of swelling of the poly dots. Atomic Force Microscopy results show that these PPE poly-dots assemble into arrays with different symmetries, depending on molecular parameters and assembly conditions.
ABSTRACT Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have... more
ABSTRACT Rigid conjugated polymers assume extended conformation in dilute solution and often behave as colloidal suspensions. When forced into a collapsed configuration, they form highly fluorescing particles, or poly-dots, which have demonstrated potential as intracellular imaging markers, as well as building blocks for light harvesting devices. The current work investigates the structure and stability of poly-dots of di-alkyl para polyphenyleneethynylene (PPE) conjugated polymers in solution and follows their assembly at interfaces. Small angle neutron scattering measurements of the poly-dots in water have shown that at low concentrations, stable unimolecular spherical poly-dots are formed with a polydispersity that corresponds to that of the polymer itself. With increasing concentration, yet, below the critical micelle concentration of these rod-like polymers in good solvents, the size and density of the NPs increases, however the spherical symmetry is retained. The nature and length of the substituents affect the internal density and the degree of swelling of the poly dots. Atomic Force Microscopy results show that these PPE poly-dots assemble into arrays with different symmetries, depending on molecular parameters and assembly conditions.
Research Interests:
Alkyl di-substituted para-polyphenyleneethylene (PPE) associates into several complex fluids in dilute solutions of toluene. At high temperature the molecules are isolated and assume extended configuration. As the temperature decreases,... more
Alkyl di-substituted para-polyphenyleneethylene (PPE) associates into several complex fluids in dilute solutions of toluene. At high temperature the molecules are isolated and assume extended configuration. As the temperature decreases, the molecules associate and eventually jam in to a fragile gel. These phases are optically active where the dynamic processes affect their optical characteristics. Inelastic Neutron Back Scattering conjunction with Neutron Spin Echo was used to characterize the dynamics on multiple length scales at different temperatures. The current talk will introduce the neutron backscattering results that follow internal dynamics within the PPE molecules as they are confined into aggregates and jams to form a fragile phase. The data will be discussed in terms of Kohlrausch-Williams-Watt model that provides characteristics time constants for the different dynamic processes.
Research Interests:
The permeation and distribution of solvents in polymer nanocomposites is governed by the way the nanoparticles (NP) associate within the matrix polymer. We have previously shown that in thin films interfacial effects affect the... more
The permeation and distribution of solvents in polymer nanocomposites is governed by the way the nanoparticles (NP) associate within the matrix polymer. We have previously shown that in thin films interfacial effects affect the distribution of the NP. The current work focuses on the response of a semi-fluorinated random copolymer, Biphenyl Perfluorocyclobutane, and Polyhedral Oligomeric Silsesquioxane (POSS) NP modified with fluorinated or protonated side chains, to presence of D2O. POSS was introduced either as a free NP or tethered to a polymer chain. We found that the presence of POSS reduces the overall uptake of D2O. It also changes the distribution of water in the film as well. In the pristine polymer film the water mainly accumulated at the substrate/polymer interface. In the nanocomposite, the water distribution is correlated with the NP distribution, where NP at the air interface minimize water penetration.
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Transport of solvents and ions within ionic polymers controls their many current and potential applications from energy related to drug delivery systems. The transport is determined by the phase structure and the interaction of the... more
Transport of solvents and ions within ionic polymers controls their many current and potential applications from energy related to drug delivery systems. The transport is determined by the phase structure and the interaction of the diffusing species with the polymers, coupled with interfacial effects. The current work presents the kinetics of penetration of long chain alcohols diffusing into rigid ionomer thin films formed by a rigid polyphenylene sulfonated ionomer, using in situ neutron reflectivity. The penetration of deuterated n-octanol and n-hexanol into ˜20nm thick films was followed as a function of time for different sulfonation levels of the polymer. As for shorter molecules, the diffusion process consists of two stages, a relatively fast one in which the film thickness increases linearly with time followed by a slow phase in which structural changes take place. With increasing sulfonation levels, the diffusion first increases and then decreases; a trend that is attributed to hydrophilic/hydrophobic balance.
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The interfacial behavior of multi block copolymer thin films results from a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the interfaces. Here... more
The interfacial behavior of multi block copolymer thin films results from a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the interfaces. Here in we report a study of thin films of ABCBA penta block copolymers, anionically synthesized, comprising of centered randomly sulfonated polystyrene block to which rubbery poly-ethylenebutalene is connected, terminated by blocks of poly-t-butylstyrene, kindly provided by Kraton. AFM and neutron reflectometry studies have shown that the surface structure of pristine films depends on film thickness and ranges from trapped micelles to thin layered films. Annealing above Tg for the styrene block results in rearrangements into relatively featureless air interface. Neutron reflectivity studies have shown that annealed films forms layers whose plane are parallel to the solid substrate with the bulky block at the air interface and the ionic block at the solid interface.
Research Interests:
The formation of hydrophilic modified disubstituted para-polyphenyleneethylene (PPE) nanoparticles (NP) complexes in aqueous media and their assemblies have been investigated. Both PPEs and gold NPs are electro-optically active.... more
The formation of hydrophilic modified disubstituted para-polyphenyleneethylene (PPE) nanoparticles (NP) complexes in aqueous media and their assemblies have been investigated. Both PPEs and gold NPs are electro-optically active. Controlling their association would allow formation of electro-optical tunable responsive materials. Small Angle Neutron Scattering (SANS) in conjunction with Atomic Force Microscopy (AFM) has been used to characterize the structures of the complexes formed. SANS studies have shown that spherical core shell NP-P complexes are formed in dilute solutions, with the gold NPs surrounded by almost fully stretched out PPE chains. With increasing the concentration of the NP-PPE complex in solution chains which consist of the basic core-shell aggregated are observed. These NP-PPE complexes were allowed to assemble at a solid surface. While the basic building block, observed by AFM, remains spherical, they assemble in different ways from random 2-d arrays to cable like structures, depending on the interaction of the NP with the PPEs and the nature of the PPE side chains.
Research Interests:
Solvent affinity drives the association of diblock co-polymers in selective solvents. The shape of the micelles is affected by the size of the blocks and their interaction with the solvent. Most experimental and theoretical studies have... more
Solvent affinity drives the association of diblock co-polymers in selective solvents. The shape of the micelles is affected by the size of the blocks and their interaction with the solvent. Most experimental and theoretical studies have investigated solutions of diblocks with a relatively low incompatibility, requiring relatively large blocks to associate. The current work introduces a small angle neutron scattering study of a highly segregated diblock-copolymer, a trifluoro propylmethyl siloxane - polystyrene (PTFPMS-PS) in solutions of d-toluene, a good solvent for the polystyrene. Studies were carried out over volume fractions of 0.1 to 0.5 of the fluorinated siloxane segment. The high degree of segregation results in association into star-like micelles with the fluorinated siloxane in the core and a swollen corona even at very low volume fractions of the fluorinated segments. The micelles exhibit unique temperature stability in comparison with aggregates formed by diblock-copolymers in a lower segregation regime. The detailed structure of these aggregates as a function of volume fraction and temperature will be discussed.
The structure of polymers within nanocomposites is strongly affected by the confinement of the polymer to the interface with the nanoparticles and the method of blending. In nanocomposites of Nylon 6 and clay particles are made by chaotic... more
The structure of polymers within nanocomposites is strongly affected by the confinement of the polymer to the interface with the nanoparticles and the method of blending. In nanocomposites of Nylon 6 and clay particles are made by chaotic blending, the strength of the chaotic flow affects the internal structure on multiple length scales, where the local structure is determined by the interfacial effects between the polymer and the nano-particle. The structural evolution as a results in alternating layers of nylon and nylon/clay regions forming two distinct interfaces, that with the clay and that of the pure nylon and the composite. The structure has been studied by X-ray, AFM and TEM at different chaotic blending strengths. At the interface with the clay particles, the polymer chains orient perpendicular to the interface. While the alpha crystalline form dominated the structure of the polymer in melts, the confinement to the layers results in an enhanced gamma form where hydrogen bonds form in between parallel nylon 6 chains dominate.