Hot-embossing experiments of polymethyl methacrylate across the glass transition temperature with variation in temperature and hold times

2012 ◽  
Vol 52 (6) ◽  
pp. 1284-1292 ◽  
Author(s):  
Kamakshi Singh ◽  
Rebecca B. Dupaix
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Polymethyl Methacrylate ◽  
Hot Embossing

High strain-rate shear response of polycarbonate and polymethyl methacrylate

1990 ◽  
Vol 429 (1877) ◽  
pp. 459-479 ◽  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
High Strain Rate ◽  
Strain Rate ◽  
Polymethyl Methacrylate ◽  
Fracture Stress ◽  
High Strain ◽  
Rate Theory ◽  
Strain Rates

The high strain rate response of polycarbonate (PC) and polymethyl methacrylate (PMMA) are measured using a split Hopkinson torsion bar for shear strain rates Ẏ from 500 s -1 to 2200 s -1 , and temperatures in the range —100°C to 200°C. The yield and fracture behaviours are compared with previous data and existing theories for Ẏ < I s -1 . We find that PC yields in accordance with the Eyring theory of viscous flow, for temperatures between the beta transition temperature T β ≈ — 100°C and the glass transition temperature T g = 147°C. At lower temperatures, T < T β , backbone chain motion becomes frozen and the shear yield stress is greater than the Eyring prediction. Strain softening is an essential feature of yield of PC at all strain rates employed. Poly methyl methacrylate fractures before yield in the high strain rate tests for T < 80°C, which is close to the glass transition temperature T g 120°C. It is found that the fracture stress for both materials obeys a thermal activation rate theory of Eyring type. Fracture is thought to be nucleation controlled, and is due to the initiation and break down of a craze at the fracture stress τ f . Examination of the fracture surfaces reveals that failure is by the nucleation and propagation of inclined mode I microcracks which link to form a stepped fracture surface. This reveals that failure is by tensile cracking and not by a thermal instability in the material. The process of shear localization is fundamentally different from that shown by steel and titanium alloys.

Physical Modelling and Identification of Polymer Viscoelastic Behaviour above Glass Transition Temperature and Application to the Numerical Simulation of the Hot Embossing Process

2013 ◽  
Vol 554-557 ◽  
pp. 1763-1776 ◽  
Author(s):  
Gang Cheng ◽  
Jean Claude Gelin ◽  
Thierry Barrière
Keyword(s):  
Numerical Simulation ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Storage Modulus ◽  
Loss Modulus ◽  
Maxwell Model ◽  
Hot Embossing ◽  
Finite Element Software ◽  
Generalized Maxwell Model

The experimental processing parameters, such as applied pressure and forming temperature have been analysed during polymer hot embossing of micro-cavities. The viscoelastic characteristics of polymer above the glass transition temperature have been investigated with the classical viscoelastic models. Generalized Maxwell Model has been used to describe polymer behaviours in the glass transition temperature range. The parameters include relaxation time, storage modulus and loss modulus of the Generalized Maxwell Model that have been introduced. The identification of polymer characteristics has been carried out through Dynamic Mechanical Analysis (DMA). The storage modulus, the loss modulus and the damping factor of the selected polymer have been obtained with different imposed frequencies. The master curve of complex modulus has been obtained by applying the time temperature superposition principle. The experimental data has been identified with optimized fitting parameters of Generalized Maxwell Model. A proper agreement between the experimental measurement and the identification of viscoelastic model is observed. The resulting constitutive equations have been implemented in finite element software in order to achieve the numerical simulation of the hot embossing process.

Fabrication of Nanochannels in Silicon and Polymers

2008 ◽  
Author(s):  
Nam-Trung Nguyen ◽  
Patrick Abgrall
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Etch Rate ◽  
Low Cost ◽  
Hot Embossing ◽  
Anodic Bonding ◽  
Fabrication Technology ◽  
Thermal Bonding ◽  
Silicon Based

This paper reports the fabrication of planar nanochannels in silicon and thermoplastic. Conventional technologies such as reactive ion etching (RIE) and anodic bonding were used for fabricating the silicon-based nanochannels, while hot embossing and thermal bonding were used for polymer-based nanochannels. Due to the limit of photolithography, the lateral dimension of the channels are kept on the order of micrometers. The depth can be controlled precisely by etch rate or deposition rate. While fabrication technologies for nanochannels in silicon and glass are established and straightforward to implement, fabrication of planar nanochannels in a plastic is challenging because of the more severe collapsing of the structure during bonding. Besides the silicon technology, we demonstrate a simple and low-cost fabrication technology of planar nanochannels by hot-embossing in a thermoplastic and bonding below the glass transition temperature.

Cellular Traction Forces Measured With Microposts Made by Hot Embossing of Polystyrene

2013 ◽  
Author(s):  
Kevin S. Bielawski ◽  
Nathan J. Sniadecki
Keyword(s):  
Glass Transition ◽  
Cell Adhesion ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Hot Embossing ◽  
Special Equipment ◽  
Moderate Amount ◽  
Lab On Chip ◽  
Common Substrate ◽  
On Chip

Polydimethylsiloxane (PDMS) has become a highly utilized tool to study the forces that cells generate, although, outside of lab on chip devices, it is not widely used and requires protein coatings to encourage cell adhesion1. Furthermore, PDMS suffers from changes in composition and stiffness with different curing conditions2. Alternatively, polystyrene is a common substrate that promotes cell adhesion and has mostly consistent properties; however, polystyrene is typically challenging to form without special equipment and expensive molds. Previously, a hot embossing method3 has been proposed to manufacture polystyrene devices using a PDMS negative mold and polystyrene chips. A moderate amount of pressure and temperatures above the glass transition temperature of polystyrene enable the polystyrene to flow into the mold. In this paper, we fabricate microposts out of polystyrene and successfully seed cells on top of the posts.

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