Double-brush polymer

Fig. 8 a-c The schematic illustrations of comb-like PEO-grafted polymer P(PEOMA) a, double grafted polymer brush P(BIEM-g-P(PEOMA)) b, and structure of hydrogel formed from polymer brush P(BIEM-g-P(PEOMA)) and a-CD c. Arrows indicate the crosslinking points [79]... 

This name covers all polymer chains (diblocks and others) attached by one end (or end-block) at ( external ) solid/liquid, liquid/air or ( internal ) liquid/liq-uid interfaces [226-228]. Usually this is achieved by the modified chain end, which adsorbs to the surface or is chemically bound to it. Double brushes may be also formed, e.g., by the copolymers A-N, when the joints of two blocks are located at a liquid/liquid interface and each of the blocks is immersed in different liquid. A number of theoretical models have dealt specifically with the case of brush layers immersed in polymer melts (and in solutions of homopolymers). These models include scaling approaches [229, 230], simple Flory-type mean field models [230-233], theories solving self-consistent mean field (SCMF) equations analytically [234,235] or numerically [236-238]. Also first computer simulations have recently been reported for brushes immersed in a melt [239]. 

First experiments which focused on the variation of the conformational properties have been performed by Brown et al. [240], who studied the role of the interactions between matrix and brush polymers (enthalpy driven brush swelling, see Eq. 59). They used a series of polystyrene (PS)-poly(methyl methacrylate) (PMMA) symmetric diblock copolymers with different blocks labeled by deuterium, placed at the interface between PMMA and poly(2,6-dimethylphenylene oxide) (PPO) homopolymers. A double brush layer was created with PMMA blocks dangling into (neutral) PMMA homopolymer and PS blocks immersed in favorably interacting PPO melt (x=Xps/ppo<0)- The SIMS profiles obtained showed that the PS side of the block copolymer is stretched by at least a factor of 2 with respect to the PMMA side. 

Zhang, M. et al. (2006) Double-responsive polymer brushes on the surface of colloid particles. J. Colloid Interface Sd., 301, 85-91. 

Zhang et al. [165,166] prepared well-defined double-responsive polymer brushes of PDMAEMA with a high density of brushes and low polydispersity (PDl 1.21). 

Figure 4.6 shows an apparatus for the fluorescence depolarization measurement. The linearly polarized excitation pulse from a mode-locked Ti-Sapphire laser illuminated a polymer brush sample through a microscope objective. The fluorescence from a specimen was collected by the same objective and input to a polarizing beam splitter to detect 7 and I by photomultipliers (PMTs). The photon signal from the PMT was fed to a time-correlated single photon counting electronics to obtain the time profiles of 7 and I simultaneously. The experimental data of the fluorescence anisotropy was fitted to a double exponential function. 

Fig. 30 Schematic representation - not to scale - of micron-sized colloidal particles coated with DNA strands with interacting sticky ends. Double helices bound to colloids form a 15-nm-thick coating which contributes to particle stability together with polymer brushes. Each helix ends with an 11-based dangling strand, either non-interacting (N) or complementary to the tails on the second type of particle (S, S ). Reproduced with permission from [136]...

Figure 3. Particle-polymer brushed surface interaction profile, (a) particle-surface contact (b) dispersion interaction (c) electrical double layer interaction osmotic polymer-brush particle interaction.

FIGURE 20.7 Gibbs energy of adhesion of a particle at a brush-coated, charged substratum surface as a function of separation distance (—), made up of four types of contributions (1) short-range particle-substratum attraction (2) dispersive attraction (3) electrostatic repulsion due to overlap of Uke-charged electrical double layers and (4) osmotic repulsion due to compression of the polymer brush. 

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