Guosheng Xue, Kun Chen, Guangyong Shen, Ziqiang Wang, Qijin Zhang, Jun Cai , Yinmei Li
Understanding the photoresponse of azobenzene polymer in different conditions is essential for the potential application of azobenzene-based technologies. Herein, the microscale, photoresponsive hybrid polymersomes (polymer vesicles) composed of binary blends of azobenzene-containing block copolymers is prepared. The Janus morphology which presents phase-separation within the surface of hybrid polymersomes is observed. The composition and photoisomerization characteristic time of different domains are studied with Laser Trapping Raman Spectroscope (LTRS) system. The results indicated that the morphology of polymersomes can be tuned by the ratio of azobenzene-containing copolymer contents. We find the photoisomerization rate of azobenzene in hybrid vesicles is marginally slower than those in pure vesicles. These experiments provide a quantitative measurement method for dynamic photoresponse of azobenzene hybrid polymersomes.
DOI
Showing posts with label Colloids and Surfaces A. Show all posts
Showing posts with label Colloids and Surfaces A. Show all posts
Thursday, October 10, 2013
Monday, June 6, 2011
Comparison of interparticle force measurement techniques using optical trapping
Timothy P. Koehler, Christopher M. Brotherton and Anne M. Grillet
Optical trapping has become a powerful and common tool for sensitive determination of electrostatic interactions between colloidal particles. Two optical trapping based techniques, blinking laser tweezers and direct force measurements, have become increasingly prevalent in investigations of interparticle potentials. The blinking laser tweezers method repeatedly catches and releases a pair of particles to gather physical statistics of particle trajectories. Statistical analysis is used to determine drift velocities, diffusion coefficients, and ultimately colloidal forces as a function of the center–center separation of the particles. Direct force measurements monitor the position of a particle relative to the center of an optical trap as the separation distance between two continuously trapped particles is gradually decreased. As the particles near each other, the displacement from the trap center for each particle increases proportional to the interparticle force. Although these techniques are commonly employed in the investigation of interactions of colloidal particles, there exists no direct comparison of these experimental methods in the literature. In this study, we compare measurements of interparticle forces applying both methods to a model system of polystyrene particles in an aerosol-OT (AOT) hexadecane solution where the screening lengths are very large. We found that the interaction forces measured using the two techniques compare quantitatively with each other and Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Additionally, our studies show that direct force measurements can be far more sensitive than previous studies have reported and nearly as sensitive as the blinking method.
DOI
Optical trapping has become a powerful and common tool for sensitive determination of electrostatic interactions between colloidal particles. Two optical trapping based techniques, blinking laser tweezers and direct force measurements, have become increasingly prevalent in investigations of interparticle potentials. The blinking laser tweezers method repeatedly catches and releases a pair of particles to gather physical statistics of particle trajectories. Statistical analysis is used to determine drift velocities, diffusion coefficients, and ultimately colloidal forces as a function of the center–center separation of the particles. Direct force measurements monitor the position of a particle relative to the center of an optical trap as the separation distance between two continuously trapped particles is gradually decreased. As the particles near each other, the displacement from the trap center for each particle increases proportional to the interparticle force. Although these techniques are commonly employed in the investigation of interactions of colloidal particles, there exists no direct comparison of these experimental methods in the literature. In this study, we compare measurements of interparticle forces applying both methods to a model system of polystyrene particles in an aerosol-OT (AOT) hexadecane solution where the screening lengths are very large. We found that the interaction forces measured using the two techniques compare quantitatively with each other and Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Additionally, our studies show that direct force measurements can be far more sensitive than previous studies have reported and nearly as sensitive as the blinking method.
DOI
Thursday, October 8, 2009
Line optical tweezers: A tool to induce transformations in stained liposomes and to estimate shear modulus
E. Spyratou, E.A. Mourelatou, A. Georgopoulos, C. Demetzos, M. Makropoulou and A.A. Serafetinides
Liposomes have been actively studied as models of cell membranes and are currently used as drug delivery systems of bioactive molecules. Liposome transformations that mimic cellular processes and are associated with their physicochemical properties have become field of interest the last decade. However, there has been little experimental work on controlled vesicle transformations by non-contact, optical handling methods.In this paper we present the use of line optical tweezers to observe liposome state transitions and transformations. Dynamic shape deformations were induced by line optical tweezers in giant stained liposomes leading to budding transition, fission and pearling creation. Under the controlled effect of line optical tweezers reversible liposome deformations were observed. The shear modulus μ of the membrane was inferred by measuring deformation of stained liposomes induced by the applied optical force. Further laser radiation caused irreversible shape deformations of liposomes, which were transformed from spherical to tubular vesicles. The ability of the selective manipulation of liposomes brings us closer to study their physicochemical properties which play a key role in cellular–liposome interactions, drug encapsulation and delivery efficiency.
Liposomes have been actively studied as models of cell membranes and are currently used as drug delivery systems of bioactive molecules. Liposome transformations that mimic cellular processes and are associated with their physicochemical properties have become field of interest the last decade. However, there has been little experimental work on controlled vesicle transformations by non-contact, optical handling methods.In this paper we present the use of line optical tweezers to observe liposome state transitions and transformations. Dynamic shape deformations were induced by line optical tweezers in giant stained liposomes leading to budding transition, fission and pearling creation. Under the controlled effect of line optical tweezers reversible liposome deformations were observed. The shear modulus μ of the membrane was inferred by measuring deformation of stained liposomes induced by the applied optical force. Further laser radiation caused irreversible shape deformations of liposomes, which were transformed from spherical to tubular vesicles. The ability of the selective manipulation of liposomes brings us closer to study their physicochemical properties which play a key role in cellular–liposome interactions, drug encapsulation and delivery efficiency.
Monday, July 13, 2009
Optical trapping studies of colloidal interactions in liquid films
R. Di Leonardo, F. Ianni, F. Saglimbeni, G. Ruocco, S. Keen, J. Leach and M. Padgett
A tightly focused light beam can stably trap small objects in three dimensions. Using spatial light modulators we can engineer the wavefront of a laser beam in such a way that, once focused by a microscope objective, it produces an almost arbitrary light intensity distribution. Arrays of optical traps can be thus generated in three-dimensional space and dynamically reconfigured. Optical traps allow direct manipulation and sensing on those length and energy scale that are most relevant in many colloidal processes. In the presence of long range interactions optical traps actually provide a unique tool of direct investigation allowing the precise relative positioning of particle pairs, far from boundaries or other particles. We have used optical trapping to directly measure two very long range interactions governing colloidal dynamics in two-dimensional fluid films: hydrodynamic interactions, which are found to decay logarithmically slow with distance, and capillary forces, whose intensity decreases as a power law with an exponent slightly smaller than one.
A tightly focused light beam can stably trap small objects in three dimensions. Using spatial light modulators we can engineer the wavefront of a laser beam in such a way that, once focused by a microscope objective, it produces an almost arbitrary light intensity distribution. Arrays of optical traps can be thus generated in three-dimensional space and dynamically reconfigured. Optical traps allow direct manipulation and sensing on those length and energy scale that are most relevant in many colloidal processes. In the presence of long range interactions optical traps actually provide a unique tool of direct investigation allowing the precise relative positioning of particle pairs, far from boundaries or other particles. We have used optical trapping to directly measure two very long range interactions governing colloidal dynamics in two-dimensional fluid films: hydrodynamic interactions, which are found to decay logarithmically slow with distance, and capillary forces, whose intensity decreases as a power law with an exponent slightly smaller than one.
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