Julie L. P. Jessop

Research Interests:
polymers
microlithography
spectroscopy

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My research interests revolve around polymers and the use of spectroscopic techniques (fluorescence, absorption, Raman scattering, etc.) for in-situ and on-line characterization of these systems. These techniques enable superior quality control and process optimization in chemical processes to be made on-line during the processing run, rather than off-line after the process is complete. Some applications of my research include cure monitoring of polymer composites, the monitoring of acid concentration and free volume evolution in photoresists used in microlithography, the investigation of polymers produced through cationic ring-opening photopolymerizations of cyclic ethers, and understanding the effects of pigmentation in photopolymerized films and coatings.

Composites Polymer Processing
There is a continued need for in-situ and on-line characterization in composites processing. For example, on-line monitoring of photopolymerizations is extremely difficult since these reactions are typically carried out in high-speed, continuous processing formats. Likewise, traditional polymer and composites processing methods involve a series of complex chemical and physical changes that must be adequately controlled to produce products with desirable properties. In either case, inexpensive and facile methods are needed to monitor process variables, such as degree of cure or viscosity, in order to minimize defect-related losses. We are investigating means to monitor pertinent process variables and to develop control strategies that would enhance product quality and throughput for a variety of industrial processing scenarios (e.g., thin films and thick molded parts).

Characterization of Acid Mobility in Chemically Amplified Photoresists
Photolithography has enjoyed premier status as the standard microlithographic technique in the semiconductor industry for many years now. Due to the drive for ever-decreasing feature size (and the corresponding shorter wavelength light to pattern the photoresist), chemically amplified resists (CARs) are rapidly displacing all other resist technologies. These resists are based upon a photo-generated acid that triggers a deprotection reaction in which the resist is rendered soluble in aqueous base and the acid is regenerated. In this manner, each photon results in deprotection of numerous sites and is "chemically amplified." The diffusion of the acidic centers affects the accuracy of the developed circuit pattern; therefore, a fundamental understanding of the reaction-diffusion mechanism is needed to optimize and extend the range of processes using deep-UV CARs. In this research, we perform experiments that will isolate and measure the kinetic parameters and activation energies of the various steps of the reaction-diffusion process. We use various in-situ spectroscopic methods to measure acid production, micro-viscosity, film thickness, diffusivity, and reaction kinetics as a function of temperature. These experimental results will be incorporated into a fundamental model with predictive capabilities. Model predictions will be validated with linewidth measurements using microscopic techniques.

Raman Spectroscopy for Cure Monitoring of Films and Coatings
This research project provides a fundamental characterization of cationic ring-opening photopolymerization for oxiranes and oxetanes. These types of kinetic studies are necessary because cationic photopolymerizations have emerged within the last decade and have received much less attention than free radical photopolymerizations. Furthermore, cationic photopolymerizations offer important advantages for use in the films and coatings industry. For instance, oxiranes and oxetanes provide less shrinkage after cure and can achieve higher conversions as living polymers than the commonly used acrylic or vinyl ether systems. In addition, because the ring-opening polymerization of these cyclic ethers is not initiated by free radical centers, but by cationic active centers, the reaction is not inhibited by oxygen. These fundamental studies will aid in the design of reaction systems for cationic photopolymerizations of cyclic ethers.

The Effect of Pigmentation on Photopolymerization
The expanding area of radiation curing affects the film, coating and inks industries as an increasing number of systems incorporate photopolymerization technology. However, pigments added to these systems pose problems that must be addressed in order to make full use of these advancements. First of all, pigments may alter the characteristics of the coating formulation, such as contributing to its storage instability or changing its flow properties. They also affect the photocuring process since incident light is scattered or absorbed by the individual pigment particles, and some pigments even participate in photochemical reactions. The goal of this research is to investigate the physical and chemical effects pigments have upon the resulting photopolymers.

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Selected Publications

Y. Zou, S.R. Armstrong, J.L.P. Jessop, “Apparent conversion of adhesive resin in the hybrid layer, part 1:  Identification of internal standards for Raman spectroscopy and the effects of water storage,” Journal of Biomedical Materials Research Part A, accepted.

Y. Cai, J.L.P. Jessop, “Decreased Oxygen Inhibition in Photopolymerized Acrylate/Epoxide Hybrid Polymer Coatings as Demonstrated by Raman Spectroscopy,” Polymer, Vol. 47(19), 2006, pp. 6560-6566.

S.R. Armstrong, J.L.P. Jessop, M.A. Vargas, Y. Zou, F. Qian, J.A.
Campbell, D.H. Pashley, “Effects of exogenous collagenase and cholesterol esterase on the durability of the resin-dentin bond,” Journal of Adhesive Dentistry, Vol. 8(3), 2006, pp. 151-160.

S.R. Armstrong, J.L.P. Jessop, E. Winn, F.R. Tay, D.H. Pashley, “Denaturation temperatures of dentin matrices. I. Effect of demineralization and dehydration,” Journal of Endodontics, Vol. 32(7), 2006, pp. 638-641.

Y. Cai, J.L.P. Jessop, “Free Radical Photopolymerizations,” Encyclopedia of Polymer Science and Technology, Volume 10, 3rd edition, edited by J.I. Kroschwitz, John Wiley & Sons, Inc., 2004, pp. 807-837.

J.L.P. Jessop, “Expanding Our Students’ Brainpower: Idea Generation and Critical Thinking Skills,” IEEE Antennas and Propagation Magazine, Vol. 40(6), 2002, pp. 140-144.

J.L.P. Jessop, S.N. Goldie, A.B. Scranton, G.J. Blanchard, “Spectroscopic Characterization of Acid Generation and Concentration and Free Volume in 248-nm Chemically Amplified Resists,” J. Vac. Sci. Technol. B, Vol. 20, 2002, pp. 219-225.

J.L.P. Jessop, G.J. Blanchard, A.B. Scranton, “In Situ Cure Monitoring Using Fiber Optic Fluorescence Sensors,” Radtech Report, Vol. 12(4), 1998, pp. 27-32.

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Patents

G.J. Blanchard, J.L. Jessop, and A.B. Scranton. "Apparatus for in situ, non-invasive polymer cure determination," U.S. Patent #5707587, January 13, 1998.

G.J. Blanchard, J.L. Jessop, and A.B. Scranton. "Method and apparatus for in situ, non-invasive polymer cure determination," U.S. Patent #5633313, May 27, 1997.

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Recent Presentations

C.M. Comer (presenter), G.A. Aurand, J.L.P. Jessop, “Photocatalytic synthesis of difuran derivatives for use as biorenewable heat-resistant monomers,” Polymer Preprints, Vol. 48(2), 2007, pp. 877-878.

Y. Cai (speaker), J.L.P. Jessop, “Investigation of Inhibition Effects in Acrylate/Epoxide Hybrid Systems Using Raman Confocal Microscopy,” RadTech 2006 e|5 Technology Conference Proceedings, CD-ROM edition, April 2006.

C. Comer (presenter), J.L.P. Jessop, “Photoinitiated Emulsion Graft Polymerization of Synthetic Monomers to Starch,” RadTech 2006 e|5 Technology Conference Proceedings, CD-ROM edition, April 2006.

D. Kim (speaker), J.L.P. Jessop, “The role of water in photoinitiated cationic ring-opening photopolymerization of cyclohexane epoxides,” RadTech 2006 e|5 Technology Conference Proceedings, CD-ROM edition, April 2006.

Y. Zou (speaker), S.R. Armstrong, J.L.P. Jessop, “Using Raman spectroscopy to determine adhesive distribution in hybrid layer of dental bonding,” RadTech 2006 e|5 Technology Conference Proceedings, CD-ROM edition, April 2006.

Y. Cai (speaker), J. Jessop, “Effect of Water Concentration on Photopolymerized Acrylate/Epoxides Hybrid Monomer System by Raman Spectroscopy,” Polymer Preprints, Vol. 47(1), 2006, pp. 490-491.

J. Alcantar (presenter), Y. Cai, J. Jessop, “The effects of temperature, initiation light intensity, and photoinitiation systems on acrylate/epoxide hybrid photopolymerizations using Raman spectroscopy,” Polymer Preprints, Vol. 47(1), 2006, pp. 585-586.