This paper presents a 2.2-GHz low jitter sub-sampling based PLL. It uses a phase-detector/charge-pump (PD/CP) that sub-samples the VCO output with the reference clock. In contrast to what happens in a classical PLL, the PD/CP noise is not multiplied by 2 in this sub-sampling PLL, resulting in a low noise contribution from the PD/CP. Moreover, no frequency divider is needed in the locked state and hence divider noise and power can be eliminated. An added frequency locked loop guarantees correct frequency locking without degenerating jitter performance when in lock. The PLL is implemented in a standard 0.18-m CMOS process. It consumes 4.2 mA from a 1.8 V supply and occupies an active area of 0.4 0.45 mm 2. With a frequency division ratio of 40, the in-band phase noise at 200 kHz offset is measured to be 126 dBc/Hz. The rms PLL output jitter integrated from 10 kHz to 40 MHz is 0.15 ps.

The chain sequence of a poly(styrene-co-methyl acrylate) copolymer is designed to form a V-shaped gradient sequence via controlled/living radical emulsion copolymerization. This specially designed chain sequence gives this common copolymer the capacity of multishape memory. The copolymer can sequentially recover to its permanent shape from three or more previously programmed temporary shapes with the stimulus of temperature.

No abstract

Surface-initiated controlled radical polymerization has been widely used for grafting polymers from various surfaces. However, how the surface-constrained radicals are terminated remains to be further elucidated. In this work, a simple kinetic model is developed for surface-initiated atom transfer radical polymerization (SI-ATRP) with addition of excess deactivator in solution. The model describes the development of polymer layer thickness, as well as the concentrations of radical, dormant and dead chains. A simple but accurate analytical solution is obtained for the polymer layer thickness as a function of time. The model accounts for the effects of equilibrium constant, activator/deactivator concentration ratio, monomer concentration, grafting density and rate constants of propagation and termination. The model is verified with the experimental data of 2methacryloyloxythyl phosphorylcholine (MPC), methyl acrylate, acrylamide, and N-isopropylacrylamide under various conditions. In correlating thickness versus time experimental curves at different catalyst concentrations, it is clearly demonstrated that the termination of radicals on surface is facilitated by diffusion of catalyst species in solution. Although radical chains are immobilized, radical centers "migrate" and terminate through activation and deactivation reactions. The termination rate constant is therefore proportional to catalyst concentration. It is also found that the termination is influenced by chain conformation and the rate constant is grafting density dependent.

High internal phase emulsion (HIPE) living polymerization was proposed in current work. Reversible addition-fragmentation chain transfer polymerization (RAFT), one of the living radical polymerization methods, was introduced to the polymerization of HIPE for the preparation of polystyrene PolyHIPEs. Living polymerization changed the crosslinking process giving a highly homogeneous polymeric wall of PolyHIPEs. The resolving of the heterogeneity problem increased the mechanical strength of PolyHIPEs significantly with the Young's modulus reaching the theoretical value of $45 MPa, which was more than 3 times higher than that by the conventional method. Not only the open-cellular structure of PolyHIPEs was maintained but also a higher connectivity was achieved. Both the type and the concentration of RAFT agents were found to have influence on the morphology and mechanical strength of PolyHIPEs.

Properties of emulsions highly depend on the interdroplet interactions and, thus, engineering interdroplet interactions at molecular scale are essential to achieve desired emulsion systems. Here, attractive Pickering emulsion gels (APEGs) are designed and prepared by bridging neighboring particle‐stabilized droplets via telechelic polymers. In the APEGs, each telechelic molecule with two amino end groups can simultaneously bind to two carboxyl functionalized nanoparticles in two neighboring droplets, forming a bridged network. The APEG systems show typical shear‐thinning behaviors and their viscoelastic properties are tunable by temperature, pH, and molecular weight of the telechelic polymers, making them ideal for direct 3D printing. The APEGs can be photopolymerized to prepare APEG‐templated porous materials and their microstructures can be tailored to optimize their performances, making the APEG systems promising for a wide range of applications.

No abstract

The thermoresponsive PEG-based copolymer poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate) (P(MEO(2)MA-co-OEGMA)] was grafted onto a silicon wafer, and its chain conformation in aqueous solution was studied by neutron reflectometry. The effects of temperature and salt concentration on the polymer's conformation were evaluated. With increasing temperature, it was found that the polymer brushes underwent a transition from an extended state to a compressed state, and eventually a collapsed state above the lower critical solution temperature. The presence of salt significantly affected the well-extended brushes but had little effect on compressed and collapsed brushes. This PEG-based thermoresponsive surface exhibited good protein adsorption resistance. Interestingly, extended and collapsed brushes showed the same level of protein repulsion, something that was not expected.