Responsive polymer brushes types

Other sensitive PEMs have been described which respond to different stimuli. Photosensitive multilayers were prepared using polyelectrolytes functionalized with photoisomerizable azobenzene chromophores. Barrett et al. have prepared sensors, the mechanical properties of which change under Hght irradiation [22]. Solvent-responsive polymer brushes have been prepared by anchoring two types of polymers (one hydrophobic and one hydrophilic) on a wafer surface. As a function... 

SI-IMP has been used for synthesis of different types of stimuli-responsive polymer brushes that are responsive to several external stimuli, such as pFI, temperature, and ionic strength [28,58-65]. Because materials interact with their surroundings via their interfaces, the ability to fashion soft interfacial layers and tune the range, extent, and type of physicochemical interactions across interfaces is central to a variety of applications. Rahane et al. carried out sequential SI-IMP of two monomers to create bilevel poly(methacrylic acid)-Woc/c-poly(N-isopropylacrylamide) (PMAA-b-PNIPAM) block copolymer brushes that can respond to multiple stimuli [28]. They observed that each strata in the bilevel PMAA-b-PNIPAM brush retained its customary responsive characteristics PMAA being a "weak" polyelectrolyte swells as pH is increased and the thermoresponsive PNIPAM block collapses as temperature is raised through the volume phase transition temperature due to its lower critical solution temperature (LCST) behavior. As a result of ions added to make buffer solutions of various pH and because of the effect of surface confinement, the swollen-collapse transition of the PNIPAM layer occurs at a... 

Abstract This article reviews results from our group of the synthesis and characterization of diblock copolymer brushes. Results from the literature are also covered. We report a wide variety of diblock compositions and compare the miscibility of the two blocks with the tendency to rearrange in response to block-selective solvents. Also, we describe the types of polymerization methods that can be utilized to prepare diblock copolymer brushes. We have compared the molecular weight of free polymer and the polymer brush based on results from our laboratory and other research groups we have concluded that the molecular weight of the free polymer and that of degrafted polymer brushes is similar. 

The observed pH-responsive behavior may originate from the electrostatic interaction between the amine end-groups of the poly(L-alanine) bmsh and the residual amines on the silica surface in a manner similar to that described earlier for other types of surface-immobilized polymer brushes [21, 68]. It is possible that at low pH, both types of amine groups become protonated and their mutual repulsion leads to the polymer extension, as described above. Thus, at low pH, the polymer brush blocks a larger portion of the nanopore volume. As the pH is increased, the eleetrostatic... 

However, in a series of publications Ito et al. [7,23,24,26] have shown that polymer brush-decorated membranes offer a much faster response while depending on the mechanical properties of the porous membrane, they can be more mechanically robust. In these publications it was also demonstrated that different types of external stimuli, such as variation of pH, temperature, solvent quality, and ultraviolet irradiation, might be used for the control of solvent permeation through the membranes. 

Depending on the nature of the grafted chains, the membrane-brush system responds to a specific type of stimulus. Known types of stimuli-responsive polymers are PAA, which has a transition between the collapsed and swollen state around pK , and PNlPAAm, which has a pronounced tendency to swell and deswell as a function of temperature. Essentially numerous combinations can be envisioned for the fabrication of concave brushes with diverse properties, including multiblock grafted polymers [45] or mixed brushes that are sensitive to multiple stimuli [36]. 

Fig. 17 Quadri-stimuli-responsive properties of PNIPAM-b-poly (methacrylic acid)-grafted gating membrane responding to temperature, anion type, pH, and salt concentration. Black lines show the responsive nature of the PNIPAM segment and red lines show the responsive nature of the poly(methacrylic acid) segment of the polymer brush. Reproduced with permission from Qien et al. [180]...

On the basis of our experimental results presented so far, the overall viscoelastic behavior of these triblock copolymers shows an elasticity-dominance over the viscosity. After reaching the critical mass density, where the static elasticity es reaches the maximum, these triblock copolymers collapse into the subphase and form hydrated brushes and these anchored brushes may be responsible for the result that the surface viscosities drop to around the 0 value at r. A distinctive difference between two types of polymers, sample I (PEO-PPO-PEO) and sample II (PPO-PEO-PPO), is the temperature dependence of r where both static elasticity and dilational viscosity show kinds of transitions. V of sample I increases with increasing temperature while that of sample II does not change with temperature. 

The effect of silicone oil and carboxylated silicone on intraocular lenses was studied with FTIR spectroscopy. It was noticed that washing with n-pentane removed the adhered silicone oils from two types of lenses, while residual oil was detected in other cases [22], The development of sequential interpenetrating polymer network (IPN) based on poly(2-methacryloyloxyethylphosphorylcholine) and silicone was studied with FTIR spectroscopy. It was discovered that IPN possesses reduced protein absorption tendency compared to pristine silicones and can be used as a novel ophthalmic biomaterial [23]. The stimuli responsive ultra-thin diblock copolymer brushes were developed on the surface of silicone rubber and studied with FTIR spectroscopy. The authors studied the thermally-induced evolution mechanism of various interactions using... 

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