Lynn M. Walker
Professor of Chemical Engineering and Chemistry (Courtesy) and Material Science and Engineering (Courtesy)

Office: Doherty Hall A219
Phone: (412) 268-3020
Fax: (412) 268-7139
Email: lwalker@andrew.cmu.edu
Secretary: Shirley Pavlischak
    Phone: (412) 268-2251
    Email: shirleyp@andrew.cmu.edu

Biography
Research Interests
Highlights
Awards and Honors
Publications
Research Group Site

Biography

Professor Lynn Walker is currently Professor of Chemical Engineering with courtesy appointments in Chemistry and in Materials Science & Engineering. Prof. Walker received her BS Chemical Engineering degree from the University of New Hampshire in 1990 and her PhD from the University of Delaware in 1995, under the supervision of Norman Wagner. After holding a postdoctoral position at Katholieke Universiteit Leuven, Leuven Belgium, Prof. Walker joined Carnegie Mellon's Department of Chemical Engineering in 1997. Prof. Walker was a Visiting Professor during a sabbatical at Polymer IRC, University of Leeds in 2007.

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Research Interests

The objective of Prof. Walker's research is to quantify the relationship between molecular-level interactions and macroscopic fluid behavior. Her group has developed experimental tools and techniques for systematically controlling molecular-level behavior, characterizing nanoscale and microscale structure in fluid systems and quantifying rheology and flow behavior of complex fluids.

Part of the research focuses on design and control of nanoscale structure in complex fluid systems. Using a combination of synthesis and manipulation of colloidal interactions, her group is developing novel soft materials such as elongated, or wormlike, micelles based on ionic surfactants. Variation of counterions allows control of the rheology and phase behavior of these materials for a variety of applications. Further adaptation of counterion chemistry makes the use of these nanoscale structures as templates for generation of amphiphilic rod-like nanoparticles possible. Another example is recent work on using the structure inherent in block copolymers to develop spatially-structured nanocomposities. Understanding the formation of these nanocomposites allows development of applications in separation, delivery and protein stabilization.

A second research focus is the impact of viscoelasticity on deformable interfaces under flow. Many industrial processes including ink-jet printing, spraying, and blending involve deformable liquid-vapor or liquid-liquid interfaces. In all of these processes, colloidal and polymeric fluid additives add elasticity to fluids and, hence, add a second elastic behavior with very different timescales than those inherent to the interfacial process. Prof. Walker's group investigates the role of fluid elasticity on these complex processes. Current work focuses on a fundamental study of how polymeric solutions wet solid surfaces and on an applications-based study of how protein additives alter inkjet printing in the formation of three-dimensional biomimetic materials.

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Highlights

• Developed a technique for forming nanostructured hydrogels containing dispersed nanoparticles and proteins. Developing the method, defining the parameter space and providing the initial fundamental foundation made up the thesis of Dr. Danilo Pozzo (currently faculty at the University of Washington, Seattle). The work is being continued by Theresa LaFollette, an NSF fellow, who is pursuing the hypothesis that the nanostructure in these hydrogels will allow protein protection against thermal denaturation. Recent findings demonstrate the ability to utilize both spherical and cylindrical micelles to generate 2D and 3D templates. Work using cylindrical templates to organize nanorods will be started by a new student, Vicki Cheng.

• Polymerization of self-assembled media has led to the formation of a series of polyelectrolyte/surfactant assemblies with properties previously not observed in these types of systems. The thesis work of Viet Lam has demonstrated the impact of low pH environments on these aggregates and is testing the feasibility of these aggregates, and others like them, for improved matrix acidification applications in oilfield recovery.

• A collaboration with Shelley Anna has two students, Wingki Lee and Nick Alvarez, developing approaches to the use of two phase flow in microfluidic devices for chemical processing. The projects require detailed understanding of fluid mechanical phenomena so that the behavior can be harnessed to produce “nanoreactors” that have sized driven by, but decoupled from, the device sizes. Recent findings demonstrate our ability to generate submicron droplets in these reactor systems and control the size distribution of gold and platinum nanoparticles grown in microreactors.

• Recent efforts in the area of interfacial rheology have grown. Matt Reichert is spending a semester at Sandia National Labs determining the impact of surfactant polyelectrolyte aggregates on the elasticity of air-water and oil-water interfaces.

• A collaboration between workers at NETL, WVU and Dennis Prieve in Chemical Engineering on development of high temperature drilling fluids has begun. We are investigating the potential of using “nanoparticle haloing” as an approach to stabilization of particulate solutions without using polymeric or other additives that are subject to degradation.

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Awards and Honors

• NSF Career Award, 2001

• Kun Li Award for Excellence in Education, Carnegie Mellon University, 2000 and 2003

• DuPont Young Professor, 2000-2001

• NSF Postdoctoral Fellow, Katholieke Universiteit Leuven, Belgium, 1996

• Departmental Teaching Fellowship, University of Delaware, 1994

• Women of Excellence Award, University of Delaware, 1991

• Tau Beta Pi National Engineering Honor Society

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Publications

       Recent Publications

       Selected Publications

       Full Publications

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Recent Publications

*“Dynamic wetting in viscous Newtonian and Non-Newtonian fluids,” Y. Wei, S. Garoff, and L. M. Walker, Journal of Physics: Condensed Matter 21(46):464126 (2009)

“Adsorption studies of a polymerizable surfactant by optical reflectivity and quartz crystal microbalance,” C. Hodges, S. Biggs and L. M. Walker, Langmuir 25(19):11503-11508 (2009)

*“Scattering from Polymer-like Micelles,” L. M. Walker, Current Opinion in Colloid & Interface Science 14(6):451-454 (2009)

“Inkjet Printing of Growth Factor Concentration Gradients and Combinatorial Arrays Immobilized on Biologically-Relevant Substrates,” E.D. Miller, J.A.Phillippi, G.W.Fisher, P.G.Campbell, L.M.Walker and L.E.Weiss, Combi. Chemistry. & High Through. Screen. 12(6):604-618 (2009)

“Impact of fluid memory on wetting approaching the air entrainment limit,” Y. Wei, S. Garoff, and L. M. Walker J. Colloid Interface Sci. 337:619-621 (2009)

“End-Group Effects on the Properties of PEG-co-PGA Hydrogels,” S. A. Bencherif, A. Srinivasan, J. A. Sheehan, G. Chakicherla, L.M. Walker, J. O. Hollinger, K. Matyjaszewski, and N. R. Washburn, Acta Biomaterialia 5(6):1872-1883 (2009)

“Influence of cross-linker chemistry on DNA release from PEG-co-PGA hydrogels,” S.A. Bencherif, J. A. Sheehan, J. O. Hollinger, L. M. Walker, K. Matyjaszewski and N. R. Washburn, J. Biomedical Materials Research, Part A, 90A:142-153 (2009)

“Complex adsorption behavior of rod-like polyelectrolyte-surfactant aggregates,” C. S. Hodges, S. Biggs and L. M. Walker, Langmuir 25(8):4484-4489 (2009)

“A Non-gradient based Algorithm for the determination of surface tension from a pendant drop: Applicable to low Bond number drop shapes,” N. J. Alvarez, L. M. Walker and S. L. Anna, J. Coll. & Interface Sci., 333:557-562 (2009)

“The synthesis and stabilization of micron and submicron sized droplets in a microfluidic flow focusing system,” W. Lee, L. M. Walker and S. L. Anna, Physics of Fluids 21:032103 (2009)

“Characterization of surfactant partitioning in polyelectrolyte-surfactant nanorod aggregates observed with a surfactant-specific electrode,” D. M. Kuntz and L. M. Walker, Industrial & Engineering Chemistry Research, 48:2430–2435 (2009)

“End-Group Effects on the Properties of PEG-co-PGA Hydrogels,” S. A. Bencherif, A. Srinivasan, J. A. Sheehan, G. Chakicherla, L.M. Walker, J. O. Hollinger, K. Matyjaszewski, and N. R. Washburn, in revision for Biomaterials (2008)

“Influence of cross-linker chemistry on DNA release from PEG-co-PGA hydrogels,” S.A. Bencherif, J. A. Sheehan, J. O. Hollinger, L. M. Walker, K. Matyjaszewski and N. R. Washburn, J. Biomedical Materials Research, Part A, available online DOI 10.1002/jbm.a.32069 (May 2008)

“Characterization of surfactant partitioning in polyelectrolyte-surfactant nanorod aggregates observed with a surfactant-specific electrode,” D. M. Kuntz and L. M. Walker, Industrial & Engineering Chemistry Research, available online DOI: 10.1021/ie8004572 (July 2008)

“Macroscopic shear alignment of linear nanoparticle arrays in soft crystals of cylindrical polymer micelles,” D. C. Pozzo and L. M. Walker, Euro. Physical J., E: Soft Matter 26:183-189 (2008)

“Nematic phases observed in amphiphilic polyelectrolyte-surfactant aggregate solutions,” D. M. Kuntz and L. M. Walker, Soft Matter, 4:286-293 (2008)

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Selected Publications

"Shear orientation of nanoparticle arrays templated in a thermoreversible block copolymer micellar crystal," D. C. Pozzo and L. M. Walker, Macromolecules 40(16):5801-10 (2007)

"Solution behavior of rod-like polyelectrolyte surfactant aggregates polymerized from wormlike micelles," D.M. Kuntz and L. M. Walker, J. Physical Chemistry B 111(23):6417-6424 (2007)

"Dynamic Wetting of Boger Fluids," Y. Wei, G. K. Seevaratnam, S. Garoff, E. Ramé and L. M. Walker, JCIS 313:274-280 (2007)

"Quantifying Air-Atomization of Viscoelastic Fluids through Fluid Relaxation Times," Y. Christanti and L. M. Walker, Atomization & Sprays 16(7):777-790 (2006)

"Controlling Dimensions of Polymerizeable Micelles: Micelle Template versus Reaction Conditions," M. J. Gerber and L. M. Walker, Langmuir 22:941-948 (2006)

"Dose-Dependent Cell Growth in Response to Concentration Modulated Patterns of FGF-2 Printed on Fibrin," E. D. Miller, G. W. Fisher, L. M. Walker, L. E. Weiss and P. G. Campbell, Biomaterials 27:2213-2221 (2006)

"Shear Induced Gelation of Laponite-PEO Mixtures," J. Zebrowski, V. Prasad, W. Zhang, L. M. Walker and D. A. Weitz, Coll. Surf. A 213(2-3):189-197 (2003)

"The Formation of an Irreversibly Adsorbed and Organized Micelle Layer at the Solid-Liquid Interface," S. Biggs, S. R. Kline and L. M. Walker, Nanoletters 2(12):1409-1412 (2002)

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Full Publications

1. *“Dynamic wetting in viscous Newtonian and Non-Newtonian fluids,” Y. Wei, S. Garoff, and L. M. Walker, Journal of Physics: Condensed Matter 21(46):464126 (2009)

2. “Adsorption studies of a polymerizable surfactant by optical reflectivity and quartz crystal microbalance,” C. Hodges, S. Biggs and L. M. Walker, Langmuir 25(19):11503-11508 (2009)

3. *“Scattering from Polymer-like Micelles,” L. M. Walker, Current Opinion in Colloid & Interface Science 14(6):451-454 (2009)

4. “Inkjet Printing of Growth Factor Concentration Gradients and Combinatorial Arrays Immobilized on Biologically-Relevant Substrates,” E.D. Miller, J.A.Phillippi, G.W.Fisher, P.G.Campbell, L.M.Walker and L.E.Weiss, Combi. Chemistry. & High Through. Screen. 12(6):604-618 (2009)

5. “Impact of fluid memory on wetting approaching the air entrainment limit,” Y. Wei, S. Garoff, and L. M. Walker J. Colloid Interface Sci. 337:619-621 (2009)

6. “End-Group Effects on the Properties of PEG-co-PGA Hydrogels,” S. A. Bencherif, A. Srinivasan, J. A. Sheehan, G. Chakicherla, L.M. Walker, J. O. Hollinger, K. Matyjaszewski, and N. R. Washburn, Acta Biomaterialia 5(6):1872-1883 (2009)

7. “Influence of cross-linker chemistry on DNA release from PEG-co-PGA hydrogels,” S.A. Bencherif, J. A. Sheehan, J. O. Hollinger, L. M. Walker, K. Matyjaszewski and N. R. Washburn, J. Biomedical Materials Research, Part A, 90A:142-153 (2009)

8. “Complex adsorption behavior of rod-like polyelectrolyte-surfactant aggregates,” C. S. Hodges, S. Biggs and L. M. Walker, Langmuir 25(8):4484-4489 (2009)

9. “A Non-gradient based Algorithm for the determination of surface tension from a pendant drop: Applicable to low Bond number drop shapes,” N. J. Alvarez, L. M. Walker and S. L. Anna, J. Coll. & Interface Sci., 333:557-562 (2009)

10. “The synthesis and stabilization of micron and submicron sized droplets in a microfluidic flow focusing system,” W. Lee, L. M. Walker and S. L. Anna, Physics of Fluids 21:032103 (2009)

11. “Characterization of surfactant partitioning in polyelectrolyte-surfactant nanorod aggregates observed with a surfactant-specific electrode,” D. M. Kuntz and L. M. Walker, Industrial & Engineering Chemistry Research, 48:2430–2435 (2009)

12. “A Non-gradient based Algorithm for the determination of surface tension from a pendant drop: Applicable to low Bond number drop shapes,” N. J. Alvarez, L. M. Walker and S. L. Anna, accepted JCIS (2008)

13. “Complex adsorption behavior of rod-like polyelectrolyte-surfactant aggregates,” C. S. Hodges, S. Biggs and L. M. Walker, in revision Langmuir (2008)

14. “End-Group Effects on the Properties of PEG-co-PGA Hydrogels,” S. A. Bencherif, A. Srinivasan, J. A. Sheehan, G. Chakicherla, L.M. Walker, J. O. Hollinger, K. Matyjaszewski, and N. R. Washburn, in revision for Biomaterials (2008)

15. “The synthesis and stabilization of micron and submicron sized droplets in a microfluidic flow focusing system,” W. Lee, L. M. Walker and S. L. Anna, accepted Physics of Fluids (Dec 2008)

16. “Inkjet Printing of Growth Factor Concentration Gradients and Combinatorial Arrays Immobilized on Biologically-Relevant Substrates,” E.D. Miller, J.A.Phillippi, G.W.Fisher, P.G.Campbell, L.M.Walker and L.E.Weiss, accepted Combi. Chemistry. & High Throughput. Screen. (to appear March 2009)

17. “Influence of cross-linker chemistry on DNA release from PEG-co-PGA hydrogels,” S.A. Bencherif, J. A. Sheehan, J. O. Hollinger, L. M. Walker, K. Matyjaszewski and N. R. Washburn, J. Biomedical Materials Research, Part A, available online DOI 10.1002/jbm.a.32069 (May 2008)

18. “Characterization of surfactant partitioning in polyelectrolyte-surfactant nanorod aggregates observed with a surfactant-specific electrode,” D. M. Kuntz and L. M. Walker, Industrial & Engineering Chemistry Research, available online DOI: 10.1021/ie8004572 (July 2008)

19. "Macroscopic shear alignment of linear nanoparticle arrays in soft crystals of cylindrical polymer micelles,” D. C. Pozzo and L. M. Walker, Euro. Physical J., E: Soft Matter 26:183-189 (2008)

20. “Nematic phases observed in amphiphilic polyelectrolyte-surfactant aggregate solutions,” D. M. Kuntz and L. M. Walker, Soft Matter, 4:286-293 (2008)

21. “Wormlike Micelles as Templates for Polymerization,” L. M. Walker and D. M. Kuntz, Current Opinion in Colloid & Interface Science 12(3):101-105 (2007)

22. “Polymerized rod-like micelle adsorption at the solid-liquid interface,” S. Biggs, M. Labarre, C. Hodges, L. M. Walker and G. Webber, Langmuir 23(15):8094-8102 (2007)

23. “Shear orientation of nanoparticle arrays templated in a thermoreversible block copolymer micellar crystal,” D. C. Pozzo and L. M. Walker, Macromolecules 40(16):5801-10 (2007)

24. “Solution behavior of rod-like polyelectrolyte surfactant aggregates polymerized from wormlike micelles,” D.M. Kuntz and L. M. Walker, J. Physical Chemistry B 111(23):6417-6424 (2007)

25. “Multisegmented Block Copolymers by “Click” Coupling of Polymers Prepared by ATRP,” P. L. Golas, N. V. Tsarevsky, B. S. Sumerlin, L. M. Walker and K. Matyjaszewski, Australian J. Chemistry 60(6):400-404 (2007)

26. “Dynamic Wetting of Boger Fluids,” Y. Wei, G. K. Seevaratnam, S. Garoff, E. Ramé and L. M. Walker, JCIS 313:274-280 (2007)

27. “Dynamic Wetting by Non-Newtonian Fluids: Shear Thinning Fluids,” G. K. Seevaratnam, Y. Suo, E. Ramé, L. M. Walker and S. Garoff, Physics of Fluids 19:012103 (2007)

28. “Small angle neutron scattering of silica nanoparticles templated in PEO-PPO-PEO cubic crystals,” D. C. Pozzo and L. M. Walker, Coll. Surfaces A (2007), 294:117-129

29. “Quantifying Air-Atomization of Viscoelastic Fluids through Fluid Relaxation Times,” Y. Christanti and L. M. Walker, Atomization & Sprays 16(7):777-790 (2006)

30. “Controlling Dimensions of Polymerizeable Micelles: Micelle Template versus Reaction Conditions,” M. J. Gerber and L. M. Walker, Langmuir 22:941-948 (2006)

31. “Dose-Dependent Cell Growth in Response to Concentration Modulated Patterns of FGF-2 Printed on Fibrin,” E. D. Miller, G. W. Fisher, L. M. Walker, L. E. Weiss and P. G. Campbell, Biomaterials 27:2213-2221 (2006)

32. “Engineered Spatial Patterns of FGF-2 Immobilized on Fibrin Direct Cell Organization,” P. G. Campbell, E. D. Miller, G. W. Fisher, L. M. Walker and L. E. Weiss, Biomat. 26:6762-6770 (2005)

33. “Three-dimensional nanoparticle arrays templated by self-assembled block-copolymer gels,” D. C. Pozzo and L. M. Walker, Macromolecular Symposium 227(1):203-210 (2005)

34. “A Bayesian Modeling Approach to Computer-Aided Experimental Design of Heterogeneous Matrices for Tissue Engineering Applications,” L. E. Weiss, C. H. Amon, E. D. Miller, D. Romero, I. Verdinelli, L. M. Walker and P. G. Campbell, Computer-Aided Design 37(11):1127-1139 (2005)

35. “Rheology and Phase Behavior of Copolymer-Templated Nanocomposite Materials,” D. C. Pozzo, K. R. Hollabaugh and L. M. Walker, J. Rheology 49(3):759-782 (2005)

36. “Dynamic Wetting of Inelastic Polymer Melts,” G. K. Seevaratnam, L. M. Walker, E. Ramé and S. Garoff, J. Coll. & Interface Science 284:265-270 (2005)

37. “Characterization of Rod-Like Aggregates Generated from a Cationic Surfactant and a Polymerizable Counterion,” M. J. Gerber, S. R. Kline and L. M. Walker, Langmuir 20(20):8150-8516 (2004)

38. “Reversible Shear Gelation of Clay-Polymer Dispersions” D. C. Pozzo and L. M. Walker Colloids & Surfaces A 240:187-198 (2004)

39. “Rheology of Transient Networks Containing Hydrophobically Modified Cellulose, Anionic Surfactant and Colloidal Silica: Role of Selective Adsorption,” K. D. Berglund, M. T. Truong, T. M. Przybycien, R. D. Tilton and L. M. Walker, Rheol. Acta 43(1):50-61 (2004)

40. “The Adsorption of Polymerized Rod-like Micelles at the Solid-Liquid Interface,” S. Biggs, S. R. Kline and L. M. Walker, Langmuir 20(4):1085-1094 (2004)

41. “Shear Induced Gelation of Laponite-PEO Mixtures,” J. Zebrowski, V. Prasad, W. Zhang, L. M. Walker and D. A. Weitz, Coll. Surf. A 213(2-3):189-197 (2003)

42. “The Formation of an Irreversibly Adsorbed and Organized Micelle Layer at the Solid-Liquid Interface,” S. Biggs, S. R. Kline and L. M. Walker, Nanoletters 2(12):1409-1412 (2002)

43. “Effect of Fluid Relaxation Time of Dilute Polymer Solutions on Jet Break up due to a Forced Disturbance,” Y. Christanti and L. M. Walker, J. Rheology 46(3):733-748 (2002)

44. “Quantifying the Importance of Micellar Microstructure and Electrostatic Interactions on the Shear-Induced Structural Transition of Cylindrical Micelles,” M. T. Truong and L. M. Walker Langmuir 18:2024 (2002)

45. “Coalescence Analysis through Small-Angle Light Scattering,” B. E. Priore and L. M. Walker, AIChE Journal 47:2644-2652 (2001)

46. “Rheology and Structure of Wormlike Micelles,” L. M. Walker, Current Opinion in Coll. & Interface Science 6(5-6):451-456 (2001)

47. “Surface Tension Driven Jet Break Up of Strain-Hardening Polymer Solutions,” Y. Christanti and L. M. Walker, J. NonNewtonian Fluid Mech. 100:9-26 (2001)

48. “SALS Analysis of Morphology Development of a Model Immiscible Polymer Blend in Transient Slit-Contraction Flows,” B.E.Priore and L.M.Walker, J.Rheology 45:383-402 (2001)

49. “Controlling the Shear-Induced Structural Transition of Rod-like Micelles Using Nonionic Polymer,” M. T. Truong and L. M. Walker, Langmuir 16:7991-7998 (2000)

50. “Orthogonal and Parallel Superposition Measurements on Lyotropic Liquid Crystalline Polymers”, L. M. Walker, J. Vermant, P. Moldenaers and J. Mewis, Rheologica Acta 39:26-37 (2000)

51. “Shear-Thickening Dilute Surfactant Solutions: the Equilibrium Structure as Studied by Small-Angle Neutron Scattering,” R. Gamez-Corrales, J.-F. Berret, L. M. Walker and J. Oberdisse, Langmuir 15:6755-6763 (1999)

52. “Orthogonal versus Parallel Superposition Measurements”, J. Vermant, L. Walker, P. Moldenaers and J. Mewis, J. Non-Newtonian Fluid Mech. 79:173-189 (1998)

53. “Small-Angle Light Scattering Study of Break-up in Immiscible Polymer Blends and Emulsions”, J. Mewis, Y. Hong, P. van Puyvelde, P. Moldenaers and L. Walker, Chem. Eng. Sci. 53:2231-2239(1998)

54. “Flow-Structure Relationship of Shear Thickening Surfactant Solutions”, J.-F. Berret, R. Gamez-Corrales, J. Oberdisse, L.M. Walker and P. Lindner, Europh. Lett. 41:677-682 (98)

55. “In Situ Analysis of the Defect Texture in Liquid Crystal Polymer Solutions Under Shear”, L.M. Walker, W. A. Kernick III and N. J. Wagner, Macromolecules 30:508-514 (1997)

56. “Macroscopic Response of Wormlike Micelles to Elongational Flow”, L.M. Walker, P.Moldenaers and J.-F. Berret, Langmuir 12:6309-6314 (1996).

57. “Concentration Effects on the Rheology and Texture of PBG/m-cresol Solutions”, L.M. Walker, M. Mortier and P. Moldenaers, J. Rheology 40:967-981 (1996).

58. “SANS Analysis of the Molecular Order in Poly(?-benzyl L-glutamate)/Deuterated Dimethylformamide (PBLG/d-DMF) under Shear and During Relaxation”, L.M. Walker and N.J. Wagner, Macromolecules 29:2298-2301 (1996).

59. “The Rheology of Concentrated PBLG Solutions”, L. M. Walker, N. J. Wagner, R.G. Larson, P.A. Mirau and P. Moldenaers, J. Rheology 39:925-952 (1995).

60. “The Structure of Isotropic Solutions of Rigid Macromolecules via SANS: PBLG/d-DMF”, N. J. Wagner, L.M. Walker and B. Hammouda, Macromolecules 28:5075-5081 (1995).

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