The effect of graphene oxide on UV curing kinetics and properties of SU8 nanocomposites

Abstract

In the present study SU8 nanocomposites were prepared by incorporating graphene oxide (GO), and its effect on the UV curing kinetics, morphology, electrical, hardness and thermal properties of the nanocomposites were investigated at different loading levels of GO (0.1 − 3 wt%). Studying the reaction kinetics of the UV curing process by means of real-time infrared spectroscopy showed that the polymerization rate and the final conversion of epoxy groups was related to the loading level of GO in the nanocomposites. An autocatalytic kinetics model of the curing reaction confirmed the effect of GO nanoparticles on the curing rate constant (k), the order of the initiation reaction (m) and the ultimate conversion of the UV-cured nanocomposites. Appropriate experimental observations indicated that dispersion of GO within the resin plays a critical role on the cure kinetics and final conversion. The results of the kinetics modeling and morphological observations showed that the curing rate constant of the nanocomposites is highly dependent on the GO content and its dispersion state, indicating that GO prevents epoxy resin crosslinking by photoinitator deactivation. Moreover, oxygen functionalities, such as hydroxyl and carboxyl groups, on the surface of GO facilitate interfacial interactions between epoxy groups from the matrix and GO. Electrical conductivity measurements demonstrated that the UV-induced photo-cured GO filled resins are conductive SU8 nanocomposites. It was observed that the thermal stability of the nanocomposites is enhanced due to the dispersion of GO in the matrix. Moreover, the microhardness analysis showed that addition of GO to neat SU8 increases the mechanical hardness of the nanocomposite.

3D printing of optical materials: an investigation of the microscopic properties

“…An almost linear decrease of both the quantities is observed up to an incident laser power of about 0.7 mW, whereas they remain almost constant for values of the incident power in the range 0.8-1.1 mW. Here, various effects are expected to contribute and to affect the observed behavior, involving the absorption of incident light by photoinitiators and production of protonic acid, which triggers the cationic polymerization [27,28]. At this stage, local heating effects cannot be ruled out, which can in turn lead to local changes in refractive index and density.…”

“…The complex trend of the time evolution of the light intensity backscattered by UV-cured SU8 reflects the various stages of photopolymerization. SU8 curing is known to proceed through a first stage where protonic acids are produced by the interaction with UV light, followed by a second stage where cationic polymerization occurs [27,28]. An effective approach for describing the polymerization kinetics is to adopt for the cluster concept for linked regions formed during the polymerization, using the well-known mathematical model for cluster-cluster aggregation based on Smoluchowski equation system [30].…”

“…SU8 has been also employed in laser-based 3D printing processes, exploiting both linear and nonlinear absorption [25,26], with minimum feature size down to 190 nm. The photopolymerization kinetics of SU8 has been studied by various methods [27,28], which provided the temporal evolution of the ensemble-averaged, macroscopic process. For instance, both catalytic and retarding effects have been highlighted for the polymerization kinetics by using nanomaterials (dielectric nanoparticles and graphene) embedded in SU8.…”

Evaluation on Curing Properties and Kinetics of Isophthalonitrile Oxide

“…In addition, the parameter of reaction series n is usually used to describe the complexity degree of the curing reaction system. In this work, Kissinger, Owaza and Crnae e quations were used to obtain the linear relation diagrams of ln(β/T 2 p ) and lnβ to 1/T p , and then the curves were processed by linear fi tting method [27][28] . Finally, the values of the apparent activation energy E a and the reaction order n of the system were obtained through the above analysis and calculation.…”

Laser Actuated Microgripper Using Optimized Chevron-Shaped Actuator

“…The microgripper could be actuated remotely to realize an opening of 30 µm using a focused laser beam to heat up a connection spot between two beams in the chevron-shaped structure. However, a common problem when utilizing the photothermic behavior of polymeric actuators is their low optical absorbance [21], which drastically reduces the overall displacement of such actuators. Since chevron-shaped actuators can be fabricated with common microelectromechanical systems (MEMS) fabrication techniques, a viable workaround is to use metallic coating to enhance the optical absorbance.…”