Copyright 2009 by the American Chemical Society VOLUME 113, NUMBER 12, MARCH 26, 2009

In Memory of Pierre-Gilles de Gennes

This special issue of the Journal of Physical Chemistrycontains research articles on the properties of soft matterspolymers, colloids, liquid crystals, surfactant self-assembly,wetting, and biologically inspired materials. As mentioned inthe biography of de Gennes, our understanding of these systemswas, in many cases, formed and, in all cases, vastly informedby the concepts and analogies that he introduced. Some of thepapers published here are directly related to de Gennes’particular contributions, and we mention a few representativeexamples of such papers.

De Gennes began his career with the study of superconduc-tivity, and a study of conductivity on quantum networks is alsorepresented in this special issue in a paper by Aharony andEntin-Wohlman.1

A problem considered in his classic text on polymers2 is apolymer near a planar surface; this was later extended to treatthe polymer brush in which the macromolecules are tethered atone end to a wall.3 The paper in this issue by Ivanov et al.4

uses simulation techniques to elucidate the phase diagram for asingle polymer tethered to a planar surface with a long-rangeattractive potential. Novel phases including those with nematicorder are found. Depletion interactions in polymer solutions arediscussed in the paper by Odijk5 to explain the effects ofpolymers on protein precipitation. Charged polymers along withtheir associated counterions in solution can form polyelectrolytebrushes; the coupling of the counterion concentration with thepolymer conformational degrees of freedom make this problemparticularly rich. Dunlop et al.6 present experimental measure-ments that characterize the normal and shear forces betweentwo such brush layers; bridging effects can lead to high shear

forces. Tension effects in brushes are discussed in the paper byPanukov et al.7 The scaling properties of polymers were animportant part of de Gennes’s contributions to both the cultureand practice of soft matter physics, and the paper by Cohen etal.8 shows how both hydrophobic and hydrophilic polymers obeythe same, complete scaling equation of state. The competitionof polymerization and self-assembly is discussed in the paperby Dudowicz et al.9

The physical properties of biological macromolecules are anatural outgrowth of our understanding of simpler, syntheticpolymers. Nelson and Chakrabarti10 use a model introduced byde Gennes for the rupture of force in DNA hybridization topredict the mechanical failure of DNA under shear. de Gennes’stheories of polymer dynamics motivated a theoretical study ofthe kinetics of thermal renaturation and hybridization of DNAin the paper by Sikorav et al.11 The ideas introduced by deGennes to model the dynamics of gels are extended to active,biological gels (actin networks and molecular motors) in thepaper by Levine and MaKintosh.12 An elaboration of deGennes’s work on forces acting on polymers is used to predictthe force on a polymer that is partially confined to a tube, asdiscussed by Prinsen et al.;13 this study is relevant to understandDNA ejection from virus capsids. A Flory theory for the foldingof RNA molecules is presented in the paper by Schwab andBruinsma.14

De Gennes’s classic book on liquid crystals15 presented acoherent description of their physics using the language of phasetransitions. Among other innovations was his introduction of atwo-component, complex order parameter for liquid-crystallinephase transitions (nematic-smectic A and smectic A-smectic

10.1021/jp900844c CCC: $40.75 2009 American Chemical SocietyPublished on Web 03/19/2009

C), analogous to those used to analyze transitions in supercon-ductivity and superfluidity. In particular, the spatial variationof the liquid-crystalline order parameter in the layered, smecticphase shows interesting similarities with superconductors;smectic layers expel twist deformations in their bulk in the sameway that superconductors expel magnetic fields. The paper byBarry et al.16 reports on a direct observation of the finite-scalepenetration of twist at the edge of a single isolated smectic Alayer of virus particles. de Gennes also showed how smecticand nematic order are coupled; however, this coupling cansometimes be eliminated by the incorporation of gels, as shownin the work of Garland and Iannacchione.17 Consequences ofnematic ordering are readily detected in magnetic resonance lineshapes and can be exploited to obtain precise phase diagramsof lyotropic liquid crystals, as shown by Smith and Freed.18

The onset of smectic positional ordering at air-liquid interfacescan be investigated using X-ray reflectivity, as discussed byPershan,19 while X-ray studies of nematic ordering have beenreported by Acharya et al.20 Another interesting surface effectis described in the paper by Delabre et al.,21 in which defectpatterns in nematic liquid crystals at liquid interfaces areobserved. The study of the synergetic properties of nematicelastomers was a field that was “created” by de Gennes, asdescribed by Lubensky and Fangfu.22 Their paper predicts thephase diagram for systems subjected to aligning or stress fieldsalong orthogonal directions.

The review article23 by de Gennes on wetting opened the eyesof the physics and physical chemistry communities to the richset of challenges posed by this phenomenon. One of thesedifficult problems is the full understanding of contact anglehysteresis, which is the difference in the advancing and recedingcontact angles. This is generally mediated by defects, and thepaper by Reyssat and Quere24 focuses on how hysteresis dependson the defect density in a system in which water is placed ona surface with hydrophobic defects such as micropillars, inwhich the edges at the tops of the pillars form strong pinningsites for the contact line. Wetting and adhesion are topics whoseinterrelation was studied by de Gennes, and the work ofVagharchakian et al.25 describes a method for characterizingvery weakly adhesive surfaces. The stability of thin films wasalso treated by de Gennes,26 and the paper by Langevin et al.27

focuses on stratification in polyelectrolytes.Soft matter systems often present novel paradigms for the

understanding of many-body, interacting systems in which the“particles” are in the nanometer to micron range and whereclassical physics governs the interparticle interactions. Aparticularly interesting example, discussed in a pioneering paperby de Gennes and Pincus,28 predicted that polymer-like, flexiblechains could be formed by colloidal dispersions of magneticparticles. These ferrofluids can show a variety of interestingmodulated phases in the presence of magnetic fields, as reviewedin the article by Andelman and Rosensweig29 that also presentsother aspects of patterning. The dynamics of ferrofluids areslowed down by hydrodynamic interactions, as shown in thelattice Boltzman simulations of Kim et al.30 Planken et al.31

present ultracentrifugation measurements of magnetic colloidsand show that the de Gennes-Pincus theory cannot reproducetheir results since they are sensitive to the short-range correla-tions. Analogues of fundamental statistical mechanics in granularmaterials are presented in a paper by Blumenfeld and Edwards.32

The self-assembly of amphiphilic molecules and their mac-romolecular analogues, block copolymers, is another area inwhich de Gennes made seminal contributions. His study33 with

Taupin on bicontinuous microemulsions focused on the role ofthe membrane persistence length (in analogy with semiflexiblepolymers) and outlined the conditions under which one wouldexpect a bicontinuous phase. The paper by Ellison et al.34

describes how polydisperse block copolymer mixtures can formbicontinous phases. The interactions of fluctuating membranesand surfaces uses concepts introduced by de Gennes to studysmectic liquid crystals, and Lee et al.35 present a study of redblood cell undulations on patterned surfaces. An extension ofmembrane physics to the crumpling of elastic, solid membranesis presented in the paper by Witten.36

These papers are just a sample of the research included inthis volume. Much or even most of this work would possiblynot have been dreamed of without the visionary role played byPierre-Gilles de Gennes. His vision will continue to inspire ourscientific dreams.

Note Added after Print Publication. References 1, 4-14,16-22, 24, 25, 27, 29-32, and 34-36 should have been J.Phys. Chem. B. This Special Issue Preface was published inthe March 26, 2009 issue (Vol. 113, No. 12, pp 3951-3952).The corrected electronic version was reposted on June 10, 2009,and an Addition and Correction will also be published (doi:10.1021/jp904912y).

References and Notes

(1) Aharony, A.; Entin-Wolman, O. J. Phys. Chem. B 2009, 113, 3676.(2) de Gennes, P. G. Scaling Concepts in Polymer Physics; Cornell

University Press: Ithaca, NY, 1979.(3) de Gennes, P. G. Macromolecules 1980, 13, 1069.(4) Ivanov, V. A.; et al. J. Phys. Chem. B 2009, 113, 3653.(5) Odijk, T. J. Phys. Chem. B 2009, 113, 3941.(6) Dunlop, I. E.; et al. J. Phys. Chem. B 2009, 113, 3947.(7) Panukov, S.; et al. J. Phys. Chem. B 2009, 113, 3750.(8) Cohen, J.; et al. J. Phys. Chem. B 2009, 113, 3709.(9) Dudowicz, J.; et al. J. Phys. Chem. B 2009, 113, 3920.

(10) Nelson, D.; Chakrabarti, B. J. Phys. Chem. B 2009, 113, 3831.(11) Sikorav, J. L.; et al. J. Phys. Chem. B 2009, 113, 3715.(12) Levine, A.; MacKintosh, F. J. Phys. Chem. B 2009, 113, 3820.(13) Prinsen, P.; et al. J. Phys. Chem. B 2009, 113, 3873.(14) Schwab, D.; Bruinsma, R. J. Phys. Chem. B 2009, 113, 3880.(15) de Gennes, P. G.; Prost, J. Physics of Liquid Crystals; Oxford

University Press: New York, 1995.(16) Barry, E.; et al. J. Phys. Chem. B 2009, 113, 3910.(17) Garland, C. W.; Iannacchione, G. S. J. Phys. Chem. B 2009, 113,

3901.(18) Smith, A.; Freed, J. H. J. Phys. Chem. B 2009, 113, 3957.(19) Pershan, P. J. Phys. Chem. B 2009, 113, 3639.(20) Acharya, B.; et al. J. Phys. Chem. B 2009, 113, 3845.(21) Delabre, U.; et al. J. Phys. Chem. B 2009, 113, 3647.(22) Lubensky, T. C.; Fangfu, Y. J. Phys. Chem. B 2009, 113, 3853.(23) de Gennes, P. G. ReV. Mod. Phys. 1985, 57, V3, 827.(24) Reyssat, M.; Quere, D. J. Phys. Chem. B 2009, 113, 3906.(25) Vagharchakian, L.; et al. J. Phys. Chem. B 2009, 113, 3769.(26) de Gennes, P. G. C. R. Acad. Sci., Ser. IIb 1998, 326, 331.(27) Langevin, D. J. Phys. Chem. B 2009, 113, 3972.(28) de Gennes, P. G.; Pincus, P. A. Phys. Kondens. Mater. 1970, 11,

189.(29) Andelman, D.; Rosensweig, R. J. Phys. Chem. B 2009, 113, 3785.(30) Kim, E.; et al. J. Phys. Chem. B 2009, 113, 3681.(31) Planken, K.; et al. J. Phys. Chem. B 2009, 113, 3932.(32) Blumenfeld, R.; Edwards, S. J. Phys. Chem. B 2009, 113, 3981.(33) de Gennes, P. G.; Taupin, C. J. Chem. Phys. 1982, 86, 2294.(34) Ellison, C.; et al. J. Phys. Chem. B 2009, 113, 3726.(35) Lee, S.; et al. J. Phys. Chem. B 2009, 113, 3610.(36) Witten, T. J. Phys. Chem. B 2009, 113, 3738.

Shankar B. RananavareSamuel A. Safran

Francoise Brochard-Wyart

JP900844C

3592 J. Phys. Chem. B, Vol. 113, No. 12, 2009