The development of new polymeric materials and structures relies primarily on controlled polymerizations, chain growth polymerizations that proceed without irreversible chain transfer, and chain termination. Recent advances in living radical polymerizations have led to the advancement of robust and simple polymerization methodologies. In particular, atom transfer radical polymerization (ATRP), pioneered by Sawamoto 1 and Matyjaszewski, 2 provides a convenient means of synthesizing end-functionalized and body-functionalized polymers, thereby enabling the synthesis of a variety of polymer architectures, including block copolymers, multiarmed stars, hyperbranched polymers, and polymer combs with well-defined composition and relatively low molecular weight polydispersities. 3 Many types of monomers including acrylates, methacrylates, styrenes, vinylpyridines, acrylonitrile, and acrylamides have been polymerized successfully via ATRP.Continuous molecular gradients represent chief tools for combinatorial chemistry and materials science. 4,5 These multivariant methods enable systematic variation of one or more physicochemical properties, thus enabling systematic exploration of the broad parameter space, improved efficiency, and lower cost. 6 Surface-tethered polymer structures represent an effective means of tuning the physicochemical properties of substrates. Recently, techniques, involving the patterning of polymer layers grafted to the substrate, have been developed

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Polyelectrolytes are remarkable molecules because of their smart behavior. By altering the environmental pH value, polyelectrolytes can undergo conformational transitions, which, if controlled, enable a wide range of applications. Herein, we describe experiments whereby a polyacid gel and a polybase grafted to a silicon substrate can be used as a means of demonstrating reversible switching adhesion in aqueous solution. By changing the environmental pH value, we can control in situ whether the gel adheres to the grafted layer or whether it dissociates. Such control over adhesion may have applications in actuators, microfluidics, drug delivery, personal-care products, or even in the understanding of biological materials.If we consider nonpolyelectrolytic polymers, the adhesion between a grafted polymer layer (polymer brush) and a polymer network in the molten state is due to enthalpic interactions that force the brush into the gel as well as the entropy of the brush as it maximizes its conformations by forming a random or self-avoiding walk structure. As the brush is entangled between fixed cross-links, the only way for the brush and the network to come apart and disentangle is for the brush to diffuse along its own contour. [1][2][3][4] This is prohibited, all the more so given that all of the other grafted polymers would have to perform the same disentanglement at the same time. The only way to remove the adhesion is therefore to break bonds, leaving the system unusable.Polyelectrolytes in aqueous solution, however, often undergo a transition from a hydrophobic state, where they can collapse and fall out of solution, to an extended hydrophilic state. This property makes them useful as nanoactuators when they are attached to a surface. [5,6] The properties of hydrogels in good solvent conditions are perhaps even more dramatic, with swellings greater than an order of magnitude than in their dry state routinely observed. [7] We present herein a means of using the responsiveness to the pH value of polyelectrolytes to create reversible adhesion of two surfaces by studying the interaction of a poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA, a polybase) brush-modified surface with a poly(methacrylic acid) (PMAA) gel. The brush and gel were equilibrated in water (initially at pH 7), then brought into contact, where it was found that there was good adhesion between the brush and the gel, a result previously obtained for two oppositely charged polyelectrolyte gels.[8] (The gel will not adhere to a silicon substrate without the brush at any pH value.) At equilibrium, the PMAA gel is partially charged and swollen to 112 % of its collapsed mass at pH 2 (approximately 300 % of its dry mass). There is also expected to be some charge on the PDMAEMA [9] brush, the free polymer of which has a pK a value of approximately 7. The two components of the system should be oppositely charged at the pH value at which equilibrium was achieved (pH 5.8). However, even at pH values of between 3 and 7, there is good adhesion between the br...

Summary: We report on preparing poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) gradient substrate, wherein molecular weight (MW) and grafting density (σ) of the surface‐anchored PDMAEMA chains vary continuously in two orthogonal directions. Such a specimen is used to control the assembly of charged gold nanoparticles. Increasing MW and σ of the grafted PDMAEMA cause an enhanced binding of the nanoparticles to PDMAEMA, thus leading to an orthogonal number density gradient of surface‐bound gold nanoparticles.magnified image

We study systematically the topography behavior of PHEMA-b-PMMA block as a function of the PHEMA and PMMA block lengths after selectively collapsing the top (PMMA) block by using surface-anchored assemblies of poly(2-hydroxyethyl methacrylate-b-methyl methacrylate), PHEMA-b-PMMA, block copolymer with orthogonally varying lengths of each block. Our experimental results are in excellent qualitative agreement with topology diagrams predicted by self-consistent field calculations of Zhulina and co-workers.