Stratified Polymer Grafts: Synthesis and Characterization of Layered ‘Brush’ and ‘Gel’ Structures

Abstract

The development of surface coatings with well-defi ned architecture is of particular interest in several disciplines, notably in biomaterials. Bio-organic layers on different length-scales, featuring variable composition, structure and modulus have been observed in several biological systems, such as human cartilage, mammalian skin and the nacre of oyster shells. [1][2][3] These complex systems often consist of mechanically graded structures that resist and respond to external normal and shear forces, and therefore protect underlying tissues from incurring any damage. As an example, the human epidermis consists of keratinizing epithelial cells-an elastic layer with low modulus-buried under a layer of dead cells, the stratum corneum , with higher modulus. The stratifi ed epithelium thus acts as the body's major barrier against abrasion and inhospitable environments. [ 4,5 ] In order to mimic mechanically useful structures found in nature, materials scientists have been made numerous efforts to fabricate coatings with discontinuous mechanical properties at pre-determined depths in a single multilayered architecture. These materials, unlike homogenous fi lms, have been shown to successfully redistribute contact stresses at the interface and to resist failure-inducing contact deformations. [ 6,7 ] Progress has also been made in fabricating graded morphologies of organic/ inorganic nanocomposites, thereby mimicking the approach of natural counterparts, to obtain coatings with higher toughness and modulus. [ 8 ] Despite all these efforts, the fabrication of a full-organic, polymer-based coating architecture featuring nanoscale variations of properties still represents a challenging task in polymer and materials science.The development of surface-initiated polymerization (SIP) techniques [ 9 ] has provided a promising path towards the stepwise fabrication of stratifi ed polymer fi lms. To this end, controlled-radical SIP methods incorporating sequential polymerization processes can be applied. [ 10 ] With the exception of the pioneering work of Tsukruk et al., [ 11 ] which introduced prototypes of stratifi ed polymeric fi lms, few such investigations have been reported. Moreover, the full characterization of stratifi ed fi lms, i.e. the physical and chemical analysis of the fi lm properties at different depths (for each stratum), on the supporting substrate certainly represents a challenging experimental task. Although real-space analytical techniques, such as atomic force microscopy (AFM), enable access to surface properties in two dimensions, determination of physical properties in the third dimension (from surface to bulk) can be more readily achieved by reciprocal-space-based techniques, such as grazing-incidence, small-angle scattering (GISAS), or X-ray and neutron refl ectivity-these methods are, at present, among the few that could determine the density profi le of materials perpendicular to the sample surface. However, probing the vertical architecture of polymeric nanofi lms with such techniques normally requir...

Stem‐Cell Clinging by a Thread: AFM Measure of Polymer‐Brush Lateral Deformation

“…The lateral deformability of the POEGMA brushes and the frictional properties as a function of tethered chain length were subsequently measured by FFM. We recently demonstrated that friction loops of hydrated brushes show “tilted” profiles between scanning‐direction reversal and steady sliding . The tilted section of the loops originates from the lateral deformation of hydrated, surface‐tethered chains when they are subjected to a sliding probe under load.…”

Synthesis of acrylamide-based block-copolymer brushes under flow: monitoring real-time growth and surface restructuring upon drying

“…18 We also demonstrated that the growth of homopolymer brushes can be interrupted and reinitiated multiple times without any notable loss in polymerization efficiency, which is an essential prerequisite for the successful construction of block-copolymer brushes. A further condition for the growth of such brushes is successful chain-end reinitiation with a second monomer, rather than the formation of new chains from the unreacted initiators remaining on the substrate surface, as reported by Li et al 19 In the present study, we introduce a flow system coupled with a switching valve that can seamlessly switch the monomer solutions from one to another without interrupting the polymerization process. Previously, we have demonstrated that the dispersity of the tethered polymer chains in such reaction environment is fairly low which is possible only if there is no continuous reinitiation from unreacted initiators at the surface.…”

Chemical Design of Non‐Ionic Polymer Brushes as Biointerfaces: Poly(2‐oxazine)s Outperform Both Poly(2‐oxazoline)s and PEG

“…Then anotribological properties of PLL-g-X films were assessed by lateral force microscopy (LFM), recording friction force versus applied load profiles (FfL) on the different brush films. [38,39] As displayed in Figure 4, PEOXA brushes showed the highest friction among the different films studied, probably because of their limited hydration and amphiphilic character.I nc ontrast, an improvement in the lubrication properties was found for PMOXA, PMOZI, and PEG brushes,w ith the latter two brush types displaying the lowest friction.…”