Michel M. Dumoulin

Orientation and structure of drawn poly(ethylene terephthalate)

Abstract Drawing of poly(ethylene terephthalate) (PET) films was performed from the amorphous state at different drawing rates and at 80°C. Crystallinity of the films was determined by thermal analysis and orientation of the different phases was determined by birefringence, Fourier transform infra-red ( FT i.r.) specular reflection and wide angle X-ray diffraction. The mechanical properties of the oriented films were studied by dynamic mechanical analysis. FT i.r. and X-ray results showed large orientation of the different phases ( trans conformers and crystalline phase), in contrast with refractive index measurements which showed unusually low birefringence results. The observed orientation was particularly high for draw ratios (λ) higher than 3. The orientation contribution of the non-crystalline phase was determined by combining FT i.r. and X-ray results. The trans -conformer contribution to the non-crystalline phase is shown to be very high for the high λ for which crystalline orientation was observed. A structural model consisting of a crystalline phase, a mesomorphic amorphous phase (constituted of trans conformers) and a purely amorphous phase (constituted solely of gauche conformers) is a possible representation of the observed results. Finally, the tensile modulus increased continuously with the overall orientation.

Surface modification of thermoplastics—towards the plastic biochip for high throughput screening devices

Microarrays have become one of the most convenient tools for high throughput screening, supporting major advances in genomics and proteomics. Other important applications can be found in medical diagnostics, detection of biothreats, drug discovery, etc. Integration of microarrays with microfluidic devices can be highly advantageous in terms of portability, shorter analysis time and lower consumption of expensive biological analytes. Since fabrication of microfluidic devices using traditional materials such as glass is rather expensive, there is great interest in employing polymeric materials as a low cost alternative that is suitable for mass production. A number of commercially available plastic materials were reviewed for this purpose and poly(methylmethacrylate) Zeonor 1060R and Zeonex E48R were identified as promising candidates, for which methods for surface modification and covalent immobilization of DNA oligonucleotides were developed. In addition, we present proof-of-concept plastic-based microarrays with and without integration with microfluidics.

Surface topography induces 3D self-orientation of cells and extracellular matrix resulting in improved tissue function

The organization of cells and extracellular matrix (ECM) in native tissues plays a crucial role in their functionality. However, in tissue engineering, cells and ECM are randomly distributed within a scaffold. Thus, the production of engineered-tissue with complex 3D organization remains a challenge. In the present study, we used contact guidance to control the interactions between the material topography, the cells and the ECM for three different tissues, namely vascular media, corneal stroma and dermal tissue. Using a specific surface topography on an elastomeric material, we observed the orientation of a first cell layer along the patterns in the material. Orientation of the first cell layer translates into a physical cue that induces the second cell layer to follow a physiologically consistent orientation mimicking the structure of the native tissue. Furthermore, secreted ECM followed cell orientation in every layer, resulting in an oriented self-assembled tissue sheet. These self-assembled tissue sheets were then used to create 3 different structured engineered-tissue: cornea, vascular media and dermis. We showed that functionality of such structured engineered-tissue was increased when compared to the same non-structured tissue. Dermal tissues were used as a negative control in response to surface topography since native dermal fibroblasts are not preferentially oriented in vivo. Non-structured surfaces were also used to produce randomly oriented tissue sheets to evaluate the impact of tissue orientation on functional output. This novel approach for the production of more complex 3D tissues would be useful for clinical purposes and for in vitro physiological tissue model to better understand long standing questions in biology.

Characterization of Surface Orientation in Poly(Ethylene Terephthalate) by Front-Surface Reflection Infrared Spectroscopy

The use of front-surface specular reflection FT-IR spectroscopy to characterize surface orientation in thick samples of poly(ethylene terephthalate) (PET) has been investigated. It has been shown that, even for samples whose surface uniformity is less than perfect, absorption index spectra of excellent quality are obtained from the Kramers-Kronig transformation. These spectra provide detailed information, both qualitative and quantitative, on the molecular conformation and orientation of the polymer. Of particular interest are the strongly absorbing bands such as the carbonyl and ester peaks, which are generally saturated in transmission spectra. The reflection technique opens up the possibility of obtaining new information on conformational changes and orientation in PET through a detailed study of these peaks.

The effects of stress relaxation on the structure and orientation of tensile drawn poly(ethylene terephthalate)

Tensile drawing experiments on poly(ethylene terephthalate) (PET) have shown that there is no significant strain-induced crystallisation until draw ratios around 2.3. The actual onset of strain-induced crystallisation depends on the deformation rate, and it occurs at lower draw ratios for higher draw rates. The development of strain-induced crystallisation has a significant impact on the relaxation behaviour of PET. Online birefringence measurements, during the relaxation of PET drawn to different draw ratios showed that: (a) at low draw ratios, the orientation relaxes over long periods of time and Fourier transform infrared (FTIR) spectroscopy showed that the overall orientation falls after relaxation; (b) at higher draw ratios, when significant strain-induced crystallisation has occurred, the orientation decreases over short times, of the order of 10 s and remains constant thereafter. This behaviour is probably due to the crystallites that lock in the extension of the chains in the amorphous material. Post relaxation FTIR measurements showed that the orientation increases due to annealing effect. Differential scanning calorimetry (DSC) showed that there is an increase in the crystalline fraction after relaxation for all draw ratios, which is probably due to the conversion of oriented amorphous material (trans conformers) into the crystalline phase.

Amorphous orientation of poly(ethylene terephthalate) by X-ray diffraction in combination with Fourier transform infra-red spectroscopy

Drawing of poly(ethylene terephthalate) (PET) films was performed from the amorphous state using different drawing rates at a temperature of 80°C. The crystallinity of the films was determined by thermal analysis and orientation of the different phases by specular reflection Fourier transform infra-red (FTi.r.) spectroscopy and wide-angle X-ray diffraction. The FTi.r. spectroscopic and X-ray results showed a significant orientation of the different molecular species (trans- and gauche-conformers and crystalline phase), particularly for draw ratios (λ) greater than 3. Determination of the amorphous orientation from X-ray diffraction of the amorphous phase of PET is shown to be possible. A combination of the FTi.r. results with those obtained for the X-ray orientation of the crystalline phase allowed an independent determination of the amorphous orientation. A good agreement was observed with the corrected X-ray amorphous orientation results for draw ratios greater than 3. Below this draw ratio, low orientation and crystallinity, combined with the inherent limitation of the X-ray technique and crystal imperfections, induced large discrepancies between the two results. It is also shown that the trans-conformer orientation increases steadily with draw ratio from the onset of draw and saturates rapidly, whereas that of the gauche-conformer is negligible for all draw ratios.

Orientation and conformation in poly(ethylene terephthalate) with low draw ratios as characterized by specular reflection infra-red spectroscopy

A quantitative treatment of the specular reflection spectra obtained from the surface of uniaxially drawn poly(ethylene terephthalate) samples has been performed. A procedure for correcting for the effect of surface irregularities is presented, and an overall orientation function based on the orientation and content of trans conformers is calculated. The results are correlated with mechanical modulus and crystallinity values. In addition, an unconventional dichroic ratio parameter based on a combination of two major bands is proposed. Results obtained from the Kramers-Kronig analysis and directly from the reflection spectra are discussed. Both are compared with the overall orientation function obtained before.

Residence time distribution in extruders determined by in-line ultrasonic measurements

The knowledge of residence time distribution (RTD) in industrial extruders is critical, notably when dealing with easily degradable polymers or when using extruders as chemical reactors. Many methods have been proposed for RTD determination but there are some drawbacks associated with each; they are expensive, hazardous, time consuming, or lacking sensitivity. A novel ultrasonic technique, sensitive to the filler concentration of polymer suspensions, is proposed. Ultrasonic properties (ultrasonic velocity and attenuation) were evaluated with regard to parameters such as linearity of the response, resolution of the measurement, and especially robustness to pressure and temperature variations. The attenuation, chosen for RTD evaluation along with a specific grade of calcium carbonate filler as the tracer, was then monitored to yield the RTD of the material in a twin-screw extruder, for different experimental conditions where quantity of filler utilized, as well as the method used to feed it, were changed in order to optimize the technique.

Plastic Polymers for Efficient DNA Microarray Hybridization: Application to Microbiological Diagnostics

ABSTRACT Fabrication of microarray devices using traditional glass slides is not easily adaptable to integration into microfluidic systems. There is thus a need for the development of polymeric materials showing a high hybridization signal-to-background ratio, enabling sensitive detection of microbial pathogens. We have developed such plastic supports suitable for highly sensitive DNA microarray hybridizations. The proof of concept of this microarray technology was done through the detection of four human respiratory viruses that were amplified and labeled with a fluorescent dye via a sensitive reverse transcriptase PCR (RT-PCR) assay. The performance of the microarray hybridization with plastic supports made of PMMA [poly(methylmethacrylate)]-VSUVT or Zeonor 1060R was compared to that with high-quality glass slide microarrays by using both passive and microfluidic hybridization systems. Specific hybridization signal-to-background ratios comparable to that obtained with high-quality commercial glass slides were achieved with both polymeric substrates. Microarray hybridizations demonstrated an analytical sensitivity equivalent to approximately 100 viral genome copies per RT-PCR, which is at least 100-fold higher than the sensitivities of previously reported DNA hybridizations on plastic supports. Testing of these plastic polymers using a microfluidic microarray hybridization platform also showed results that were comparable to those with glass supports. In conclusion, PMMA-VSUVT and Zeonor 1060R are both suitable for highly sensitive microarray hybridizations.

Measurements of Absolute Birefringence of Biaxially Oriented Films and Sheets On-Line or Off-Line

In this paper, we discuss the development and use of a birefringence technique for on-line or off-line quantitative measurement of orientation in transparent films, sheets, bottles, etc. Absolute values of birefringence are measured in two directions using a technique based on an incident multi-wavelength double beam and a photodiode array assembly, combined with in-house developed software. Both machine and transverse direction birefringence (relative to the normal direction) are measured quasi-simultaneously. Film and sheet thicknesses from 10 microns to 10 mm were tested and birefringence values from 0.0005 to 0.25 were measured. The technique was tested on different materials and under different conditions and several applications will be discussed.