Polymer brushes dissipation

Irfachsyad, D., Tildesley, D., Malfreyt, P. Dissipative particle dynamics simulation of grafted polymer brushes under shear. Phys. Chem. Chem. Phys. 4, 3008-3015 (2002). doi 10.1039/ B110738k... 

The friction of polymers or CMP processes can be attributed to two major sources in mixed modes deformation involving the dissipation of energy in quite a large volume around the local area of contact, and adhesion originating from the interface between the wafer and the pads (brush). The details of the deformation and adhesion will be discussed in Chapter 5, along with a clear schematic illustration. 

Polymer-matrix composites have been used as one of the most common packaging materials for encapsulating a variety of electronic components for dissipating heat [14]. In this section, 3D AlN nanowhiskers with brush-hke structure were filled into the polymer matrix to enhance its thermal conductivity. The 3D brush-hke AlN fiUers were fabricated by CS process [7a], as iUustrated in Section 3.2. The use of AlN as a filler candidate to enhance the thermal conductivity of the polymer is attributed to its attractive properties such as high thermal conductivity, high electrical resistivity, and good chemical stabihty with polymers [1]. To explore the promoting effect of the 3D brush-hke AIN fillers on thermal conductivity, three types of AIN fillers with different brush-hke filler aspect ratio were added into polymer matrix to fabricate a series of composites and their thermal conductivities were measured. The results demonstrated that the 3D brush-hke AIN nanowhiskers fillers can effectively enhance the thermal conductivity of the polymer composite. 

The present study aims to understand the influence of solvent quality on the molecular-level friction mechanism of tethered, brushlike polymers. It involves complementary adsorption studies of PLL-,g-PEG by means of optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation (QCM-D) as well as friction studies performed on the nanoscale using colloidal-probe lateral force microscopy (LFM). The adsorbed mass measured by QGM-D includes a contribution from solvent molecules absorbed within the surface-bound polymer fllm. This is in contrast to optical techniques, such as OWLS, which are sensitive only to the dry mass of a polymer adsorbed onto the surface of the waveguide.By subtracting the dry mass , derived from OWLS measurements, from the wet mass , derived from QCM-D measurements, it is therefore possible to determine the mass of the solvent per unit substrate area absorbed in the brushlike structure of PLL- -PEG, expressed as areal solvation, P. Areal solvation was varied by choosing solvents (aqueous buffer solution, methanol, ethanol, and 2-propanol) of different quality with respect to the PEG brush. The solvents were characterized in terms of the three-component Hansen solubility parameters, and these values were compared with measured areal solvation of the PEG brush. 

In this work, a silane-derivatized dithiocarbamate iniferter was utilized to prepare PMAA brushes on Si/Si02 surfaces under UV irradiation. The combination of the photoiniferter-mediated photopolymerization with a UV-LED source appears to be ideally suited to the direct preparation of polyelectrolyte brushes with minimal free polymer formation during brash synthesis. Following characterization of the PMAA brushes by means of surface-analytical techniques, such as quartz crystal micro-balance with dissipation monitoring (QCM-D), spectroscopic ellipsometry, and static contact-angle measurements, the PMAA brushes were demonstrated to enhance aqueous lubrication of Si/ Si02 under low-contact-pressure conditions. 

Figure 6. Frequency shift (black circles) and dissipation changes (gray circles) observed in QCM-D experiments during sinface-initiat, in situ polymerization of PMAA brushes from 10 vol % monomer solutions in water. After a first polymerization step, the QCM cell was rinsed with fresh monomer solution (after 100 min) before the UV-LED was switched on again (after 290 min) to induce a second polymerization step. After the UV source was switched off (after 325 min), the cell was rinsed with fresh monomer twice before pure water was continuously pumped through the system in order to remove unbound polymer.

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