Growth Mechanism, Kinetics, and Molecular Weight

Kinetically Limited Bulk Polymerization of Polymer Thin Films by Initiated Chemical Vapor Deposition

“…For the initiator, as discussed above, normal iCVD operations already demand relatively more initiator to be charged into the reactor than is typical in the liquid phase or bulk polymerization to compensate for the initiator being more volatile. This compensation is normally made in excess to the point that the initiator is generally not a limiting factor in influencing deposition kinetics . In addition, due to the free radical chain mechanism of the polymerization process, the process requires only a relatively minute amount of the initiator and resulting initiator radicals to sustain polymer chain propagation and film growth.…”

“…The lower substrate temperature promotes monomer vapor adsorption onto the surface, while the heated filaments thermally activate the initiator in the gas phase to generate reactive species (e.g., free radicals), which then initiate surface polymerization of the adsorbed monomer. − The amount of adsorbed monomer can be quantified by its saturation ratio, P m / P sat , which is defined as the ratio of the monomer partial pressure in the gas phase to the monomer vapor pressure evaluated at the temperature of the cooled substrate. The saturation ratio, which reflects the monomer concentration on the substrate surface, in turn controls the polymer film deposition rate under normal operating conditions. − Under normal iCVD conditions in which the monomer at the surface is subsaturated ( P m / P sat < 1), the rate-limiting step for iCVD polymerization has been shown to be the adsorption of the monomer onto the substrate surface. − Therefore, achieving high polymer deposition rates in iCVD typically involves lowering the substrate temperature to enhance monomer adsorption and increase P m / P sat (by reducing P sat ). , However, the need to cool the substrate can be an operational challenge for scale-up to roll-to-roll continuous iCVD reactors, where maintaining adequate surface contact of a moving substrate against a chilled platen is difficult . Furthermore, highly volatile monomers such as ethylene oxide may require cryogenic cooling to achieve reasonably low vapor pressures ( P sat = 0.1 Torr at −32 °C).…”

“…The lower substrate temperature promotes monomer vapor adsorption onto the surface, while the heated filaments thermally activate the initiator in the gas phase to generate reactive species (e.g., free radicals), which then initiate surface polymerization of the adsorbed monomer. 19 − 21 The amount of adsorbed monomer can be quantified by its saturation ratio, P m / P sat , which is defined as the ratio of the monomer partial pressure in the gas phase to the monomer vapor pressure evaluated at the temperature of the cooled substrate. The saturation ratio, which reflects the monomer concentration on the substrate surface, in turn controls the polymer film deposition rate under normal operating conditions.…”

“…The saturation ratio, which reflects the monomer concentration on the substrate surface, in turn controls the polymer film deposition rate under normal operating conditions. 19 − 21 Under normal iCVD conditions in which the monomer at the surface is subsaturated ( P m / P sat < 1), the rate-limiting step for iCVD polymerization has been shown to be the adsorption of the monomer onto the substrate surface. 20 − 25 Therefore, achieving high polymer deposition rates in iCVD typically involves lowering the substrate temperature to enhance monomer adsorption and increase P m / P sat (by reducing P sat ).…”

Data‐driven prediction and optimization of liquid wettability of an initiated chemical vapor deposition‐produced fluoropolymer

“…Using conventional reaction rate equations and parameters, the reaction kinetics can be modeled with enough accuracy 4 . However, the mechanisms that determine the growth of the worm‐like structures are currently not fully understood 3 .…”