Smart polymer brushes and their emerging applications

Peng, Shunjin; Bhushan, Bharat

doi:10.1039/c2ra20451g

Cited by 107 publications

(93 citation statements)

References 299 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[13][14][15][16][17][18][19][20] However, bottlebrush block polymers display much larger scaling exponents ( = 0.8-0.9), [21][22][23][24] consistent with extended backbone conformations. Steric repulsion between the densely grafted side chains imparts a certain bending rigidity to the backbone, which can be modeled as a wormlike chain.…”

mentioning

confidence: 99%

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

et al. 2017

View full text Add to dashboard Cite

Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z). The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

show abstract

mentioning

confidence: 99%

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

et al. 2017

View full text Add to dashboard Cite

show abstract

“…For the interaction between particles belonging to the polymer, the cut-off radius was set to the minimum of the Lennard-Jones potential r C = 6 √ 2σ ≃ 1.12σ, giving a purely repulsive force which is interpreted as a polymer in good solvent conditions. For the liquid-liquid and liquid-polymer interactions, the cut-off radius was set to twice the minimum of the potential r C = 2 6 √ 2σ ≃ 2.24σ, to include attractive interactions. This allows the formation of liquid and gas phases for temperatures below the evaporating point.…”

Section: Model and Simulation Techniquesmentioning

confidence: 99%

“…They are also used as coatings in "smart surfaces" to fine tune reversibly some property of an interface upon changes in external stimuli, for example, PH [5], temperature, solvent quality [6,7]. Brushes are at the forefront of recent developments, ranging from responsive bio-interphases, controlled drug-delivery and release systems, thin films and particles, which act as sensors of minute amounts of analytes [3,6]. The geometry and curvature of the grafted surface contribute also to distinctive properties of brushes, which can be grown in planar or cylindrical geometries, in the surface of nanoparticles or into the backbone of macromolecules (bottle-brushes) [1,8].…”

Section: Introductionmentioning

confidence: 99%

“…They find important applications in colloid stabilization, lubrication, and developments where friction [4], adhesion and wetting properties are important [1]. They are also used as coatings in "smart surfaces" to fine tune reversibly some property of an interface upon changes in external stimuli, for example, PH [5], temperature, solvent quality [6,7]. Brushes are at the forefront of recent developments, ranging from responsive bio-interphases, controlled drug-delivery and release systems, thin films and particles, which act as sensors of minute amounts of analytes [3,6].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Speyer

Pastorino

2015

Soft Matter

View full text Add to dashboard Cite

We performed molecular dynamics simulations to study equilibrium and flow properties of a liquid in a nano-channel with confining surfaces coated with a layer of grafted semiflexible polymers. The coverage spans a wide range of grafting densities from essentially isolated chains to dense brushes. The end-grafted polymers were described by a bead spring model with an harmonic potential to include the bond stiffness of the chains. We varied the rigidity of the chains, from fully flexible polymers to rigid rods, in which the configurational entropy of the chains is negligible. The brushliquid interaction was tuned to obtain a super-hydrophobic channel, in which the liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter state. Equilibrium properties such us brush height and bending energy were measured, varying the grafting density and the stiffness of the polymers. We studied also the characteristics of the brush-liquid interface and the morphology of the polymers chains supporting the liquid for different bending rigidities. Non-equilibrium simulations were performed, moving the walls of the channel in opposite directions at constant speed, obtaining a Couette velocity profile in the bulk liquid. The molecular degrees of freedom of the polymers were studied as a function of the Weissenberg number. Also, the violation of the no-slip boundary condition and the slip properties were analyzed as a function of the shear rate, grafting density and bending stiffness. At high grafting densities, a finite slip length independent of the shear rate or bending constant was found, while at low grafting densities a very interesting non-monotonic behaviour on the bending constant is observed.

show abstract

“…Such polymers are widely termed 2 "cylindrical molecular brushes" due to their steric-induced stiffness and axes of symmetry. [39][40][41][42][43] These cylindrical brushes can be modeled as wormlike chains with the same average crosssectional radius (Rc) along the entire backbone. 5,[44][45][46] On the other hand, if the macromonomer and diluent copolymerize at different rates, the resulting gradient sequences are anticipated to template different side chain conformations.…”

Section: Introductionmentioning

confidence: 99%

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

et al. 2017

View full text Add to dashboard Cite

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl co-monomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over two orders of magnitude (0.36 M −1 s −1 < khomo < 82 M −1 s −1 ). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(D,L-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by non-linear least squares fitting of the instantaneous co-monomer concentrations according to the Mayo-Lewis terminal model. Indepth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r1/r2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo-and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

show abstract

Smart polymer brushes and their emerging applications

Cited by 107 publications

References 299 publications

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

Contact Info

Product

Resources

About