PGI-1, FZ Jülich, Germany.
Soft Matter. 2018 Feb 14;14(7):1142-1148. doi: 10.1039/c7sm02216f.
Adhesion between a glass ball and a polydimethylsiloxane (PDMS) sample is dependent on the PDMS cross-link density, and the transformation of the material from the uncrosslinked liquid state to the fully crosslinked solid state is investigated in this study. The physical picture reflected a gradual transition from capillary forces driven contact mechanics to the classical Johnson-Kendall-Roberts (JKR)-type contact mechanics. PDMS was produced by mixing the base fluid and a cross-linker at a ratio of 10 : 1 and allowed to slowly cross-link at room temperature with simultaneous measurement of the ball-PDMS interaction force. The PDMS sample was in the liquid state during the first ≈16 hours, and in this case the ball-PDMS interaction was purely adhesive, i.e., no repulsive interaction was observed. Later at the PDMS gel-point the cross-linked PDMS clusters percolate, converting the fluid into a soft (fluid-filled) poroelastic solid. In the transition period, PDMS appears similar to pressure-sensitive adhesives. There we observe so-called "stringing" and permanent deformation of the material impacted by the ball. At room temperature, it takes more than ∼100 hours for PDMS to fully cross-link that can be confirmed by the comparison with the earlier-studied reference PDMS produced at elevated temperatures.
玻璃球与聚二甲基硅氧烷（PDMS）样品之间的粘附取决于 PDMS 的交联密度，本研究调查了该材料从未交联的液态到完全交联的固态的转变。所反映的物理图像是从由毛细力驱动的接触力学到经典的 Johnson-Kendall-Roberts（JKR）型接触力学的逐渐转变。PDMS 通过将基础流体和交联剂以 10:1 的比例混合并在室温下缓慢交联同时测量球-PDMS 相互作用力来制备。在最初的 ≈16 小时内，PDMS 样品处于液态，在这种情况下，球-PDMS 相互作用纯粹是粘附的，即没有观察到排斥相互作用。后来在 PDMS 凝胶点处，交联的 PDMS 簇渗透，将流体转化为软（充满流体）的多孔弹性固体。在过渡期间，PDMS 类似于压敏粘合剂。在这种情况下，我们观察到所谓的“拉丝”和材料被球撞击时的永久变形。在室温下，PDMS 要经过超过 ∼100 小时才能完全交联，这可以通过与在较高温度下制备的早期研究的参考 PDMS 进行比较来证实。
