11 research outputs found
Elementary edge and screw dislocations visualized at the lattice periodicity level in smectic phase of colloidal rods
We report on the identification and quantitative characterization of
elementary edge and screw dislocations in a colloidal smectic phase of
tip-labeled rods. Thanks to the micrometer layer spacing, direct visualization
of dislocations has been performed at the \textit{smectic periodicity scale} by
optical fluorescence microscopy. As a result, the displacement field around an
edge dislocation has been experimentally established and compared with the
profile predicted by elastic theory. Elementary screw dislocations have been
also evidenced, for which the core size as well as the \textit{in situ}
handedness have been determined. Self-diffusion experiments performed at the
individual particle level reveal for the first time nematic-like or "melted"
ordering of the defect core.Comment: 5 pages, 5 figures, accepted in PR
Directing liquid crystalline self-organization of rod-like particles through tunable attractive single tips
Dispersions of rodlike colloidal particles exhibit a plethora of liquid
crystalline states, including nematic, smectic A, smectic B, and columnar
phases. This phase behavior can be explained by presuming the predominance of
hard-core volume exclusion between the particles. We show here how the
self-organization of rodlike colloids can be controlled by introducing a weak
and highly localized directional attractive interaction between one of the ends
of the particles. This has been performed by functionalizing the tips of
filamentous viruses by means of regioselectively grafting fluorescent dyes onto
them, resulting in a hydrophobic patch whose attraction can be tuned by varying
the number of bound dye molecules. We show, in agreement with our computer
simulations, that increasing the single tip attraction stabilizes the smectic
phase at the expense of the nematic phase, leaving all other liquid crystalline
phases invariant. For a sufficiently strong tip attraction, the nematic state
may be suppressed completely to get a direct isotropic liquid-to-smectic phase
transition. Our findings provide insights into the rational design of building
blocks for functional structures formed at low densities.Comment: 13 pages, 4 figure
Structure and dynamics of rod-like colloids with patchy interaction
Les dispersions de virus filamenteux prĂ©sentent une succession d'Ă©tats cristallins liquides comprenant les phases nĂ©matique, smectique (ou lamellaire) et colonnaire. Lâauto-organisation de ces particules colloĂŻdales en forme de bĂątonnet sâest rĂ©vĂ©lĂ©e ĂȘtre essentiellement pilotĂ©e par lâentropie dont rĂ©sulte un potentiel dâinteraction entre particules purement rĂ©pulsif. Dans cette thĂšse, les propriĂ©tĂ©s structurales et dynamiques de bĂątonnets prĂ©sentant une interaction attractive directionnelle fortement localisĂ©e (interaction dite à « patch ») Ă l'une des extrĂ©mitĂ©s des particules ont Ă©tĂ© Ă©tudiĂ©es. Lâinteraction attractive locale a Ă©tĂ© obtenue en fonctionnalisant les extrĂ©mitĂ©s des virus filamenteux par greffage rĂ©giosĂ©lectif de colorants fluorescents hydrophobes qui jouent le rĂŽle de « patch » enthalpique. La force d'attraction peut ĂȘtre modulĂ©e en faisant varier le nombre de molĂ©cules de colorant liĂ©es. Nous avons montrĂ© que cette interaction à « patch » stabilise la phase smectique au dĂ©triment de la phase nĂ©matique, laissant les autres phases cristallines liquides essentiellement inchangĂ©es. En outre, la prĂ©sence de molĂ©cules de colorant fluorescent sur les extrĂ©mitĂ©s des virus permet l'observation de structures lamellaires cristal-liquides avec un contraste et une rĂ©solution exacerbĂ©s. La visualisation in situ de dĂ©fauts topologiques en phase smectique, telle des dislocations de type coin et vis, a Ă©tĂ© rĂ©alisĂ©e Ă l'Ă©chelle de la pĂ©riodicitĂ© du rĂ©seau. Le champ de dĂ©placement autour dâune dislocation coin a Ă©tĂ© Ă©tabli expĂ©rimentalement et comparĂ© au profil prĂ©dit par les thĂ©ories Ă©lastiques. Des dislocations de type vis ont Ă©galement Ă©tĂ© mises en Ă©vidence, pour lesquelles la taille du cĆur et l'helicite ont Ă©tĂ© dĂ©terminĂ©es.La dynamique des virus « patchy » et de ceux non fonctionnalisĂ©s a Ă©tĂ© Ă©tudiĂ©e par suivi temporel du dĂ©placement des particules individuelles en microscopie de fluorescence. Dans toutes les phases cristallines liquides, la diffusion de particules « patchy » s'est avĂ©rĂ©e ĂȘtre entravĂ©e. En particulier dans la phase smectique, les bĂątonnets « patchy » ont tendance Ă rĂ©sider dans les couches diffusant principalement dans la direction perpendiculaire Ă l'axe principal du virus, tandis que les bĂątonnets non fonctionnalisĂ©s prĂ©sentent une diffusion entre couches beaucoup plus prononcĂ©e. Ce comportement peut sâexplique par la plus grande valeur du potentiel smectique associĂ© et mesurĂ© expĂ©rimentalement dans les deux types de dispersion.Nous avons combinĂ© des effets de « patch » entropique et enthalpique en ajoutant des polymĂšres non-absorbants Ă la dispersion virale fonctionnalisĂ©e. Dans ce cas, les bĂątonnets sâauto-assemblent latĂ©ralement par dĂ©plĂ©tion en des clusters. La diffusion de rayons X et la microscopie optique ont Ă©tĂ© utilisĂ©es pour comparer les propriĂ©tĂ©s structurales et dynamiques des dispersions virales fonctionnalisĂ©es - ou pas - mĂ©langĂ©es Ă des polymĂšres non absorbants, et pour Ă©tablir les diagrammes de phases correspondants.En rĂ©sumĂ©, nous avons dĂ©montrĂ© un nouveau moyen efficace de contrĂŽler la structure de fluides complexes par la modifications rĂ©gio-sĂ©lective des particules constituantes.Dispersions of filamentous viruses exhibit a plethora of liquid crystalline states including nematic, smectic (or lamellar), and columnar phases. Self-organization of these rod-shaped colloidal particles has been shown to map the hard-core behavior for which the interaction potential is purely repulsive. In this thesis, the structural and dynamical properties of rods with highly localized directional attractive interaction (or âpatchinessâ) between one of the ends of the particles have been studied. Local attraction has been achieved by functionalizing the filamentous virus tips via regioselective grafting hydrophobic fluorescent dyes which act as enthalpic patch. The single tip attraction strength can be tuned by varying the number of bound dye molecules. We have shown that increasing attraction interaction stabilizes the smectic phase at the cost of nematic phase leaving all other liquid crystalline transitions unchanged. Furthermore, the fluorescent dye molecules on the viral tips enable the observation of liquid crystalline lamellar structures with improved contrast and resolution. In situ visualization of topological defects in the smectic phase such as edge and screw dislocations has been thus performed at the lattice periodicity level. The displacement field around an edge dislocation has been experimentally established and compared to the profile predicted by elastic theory. Screw dislocations have been also evidenced, for which the core size and handedness have been determined.Dynamics of patchy and pristine viruses has been investigated by tracking individual rod displacements. In all liquid crystalline phases, the self-diffusion of patchy rods has been found to be hindered compared to the self-diffusion of pristine rods. Particularly in the smectic phase, patchy rods tend to reside within the layers mainly diffusing in the direction perpendicular to the main virus axis, contrary to pristine rods whose self-diffusion between layers is far more pronounced. This behavior is explained by the higher unidimensional smectic ordering potential experimentally measured in the dispersions of patchy rods compared to that obtained for pristine rods.We have combined both entropic and enthalpic patchinesses by adding non-adsorbing polymers into tip-functionalized viral dispersions. In this case, rod sides act as entropic patchy sites due to attractive depletion interaction between them. Small angle X-ray scattering and optical microscopy techniques have been used to compare the structural and dynamical properties of pristine and tip-functionalized viral dispersions mixed with hydrophilic polymers acting as depletants agent. We have determined and compared the phase diagrams obtained for the two types of virus-polymer systems.In summary, we have demonstrated a new and efficient way to control the structure of complex fluids by implementing site-specific modifications of building blocks
Structure and dynamics of rod-like colloids with patchy interaction
Les dispersions de virus filamenteux prĂ©sentent une succession d'Ă©tats cristallins liquides comprenant les phases nĂ©matique, smectique (ou lamellaire) et colonnaire. Lâauto-organisation de ces particules colloĂŻdales en forme de bĂątonnet sâest rĂ©vĂ©lĂ©e ĂȘtre essentiellement pilotĂ©e par lâentropie dont rĂ©sulte un potentiel dâinteraction entre particules purement rĂ©pulsif. Dans cette thĂšse, les propriĂ©tĂ©s structurales et dynamiques de bĂątonnets prĂ©sentant une interaction attractive directionnelle fortement localisĂ©e (interaction dite à « patch ») Ă l'une des extrĂ©mitĂ©s des particules ont Ă©tĂ© Ă©tudiĂ©es. Lâinteraction attractive locale a Ă©tĂ© obtenue en fonctionnalisant les extrĂ©mitĂ©s des virus filamenteux par greffage rĂ©giosĂ©lectif de colorants fluorescents hydrophobes qui jouent le rĂŽle de « patch » enthalpique. La force d'attraction peut ĂȘtre modulĂ©e en faisant varier le nombre de molĂ©cules de colorant liĂ©es. Nous avons montrĂ© que cette interaction à « patch » stabilise la phase smectique au dĂ©triment de la phase nĂ©matique, laissant les autres phases cristallines liquides essentiellement inchangĂ©es. En outre, la prĂ©sence de molĂ©cules de colorant fluorescent sur les extrĂ©mitĂ©s des virus permet l'observation de structures lamellaires cristal-liquides avec un contraste et une rĂ©solution exacerbĂ©s. La visualisation in situ de dĂ©fauts topologiques en phase smectique, telle des dislocations de type coin et vis, a Ă©tĂ© rĂ©alisĂ©e Ă l'Ă©chelle de la pĂ©riodicitĂ© du rĂ©seau. Le champ de dĂ©placement autour dâune dislocation coin a Ă©tĂ© Ă©tabli expĂ©rimentalement et comparĂ© au profil prĂ©dit par les thĂ©ories Ă©lastiques. Des dislocations de type vis ont Ă©galement Ă©tĂ© mises en Ă©vidence, pour lesquelles la taille du cĆur et l'helicite ont Ă©tĂ© dĂ©terminĂ©es.La dynamique des virus « patchy » et de ceux non fonctionnalisĂ©s a Ă©tĂ© Ă©tudiĂ©e par suivi temporel du dĂ©placement des particules individuelles en microscopie de fluorescence. Dans toutes les phases cristallines liquides, la diffusion de particules « patchy » s'est avĂ©rĂ©e ĂȘtre entravĂ©e. En particulier dans la phase smectique, les bĂątonnets « patchy » ont tendance Ă rĂ©sider dans les couches diffusant principalement dans la direction perpendiculaire Ă l'axe principal du virus, tandis que les bĂątonnets non fonctionnalisĂ©s prĂ©sentent une diffusion entre couches beaucoup plus prononcĂ©e. Ce comportement peut sâexplique par la plus grande valeur du potentiel smectique associĂ© et mesurĂ© expĂ©rimentalement dans les deux types de dispersion.Nous avons combinĂ© des effets de « patch » entropique et enthalpique en ajoutant des polymĂšres non-absorbants Ă la dispersion virale fonctionnalisĂ©e. Dans ce cas, les bĂątonnets sâauto-assemblent latĂ©ralement par dĂ©plĂ©tion en des clusters. La diffusion de rayons X et la microscopie optique ont Ă©tĂ© utilisĂ©es pour comparer les propriĂ©tĂ©s structurales et dynamiques des dispersions virales fonctionnalisĂ©es - ou pas - mĂ©langĂ©es Ă des polymĂšres non absorbants, et pour Ă©tablir les diagrammes de phases correspondants.En rĂ©sumĂ©, nous avons dĂ©montrĂ© un nouveau moyen efficace de contrĂŽler la structure de fluides complexes par la modifications rĂ©gio-sĂ©lective des particules constituantes.Dispersions of filamentous viruses exhibit a plethora of liquid crystalline states including nematic, smectic (or lamellar), and columnar phases. Self-organization of these rod-shaped colloidal particles has been shown to map the hard-core behavior for which the interaction potential is purely repulsive. In this thesis, the structural and dynamical properties of rods with highly localized directional attractive interaction (or âpatchinessâ) between one of the ends of the particles have been studied. Local attraction has been achieved by functionalizing the filamentous virus tips via regioselective grafting hydrophobic fluorescent dyes which act as enthalpic patch. The single tip attraction strength can be tuned by varying the number of bound dye molecules. We have shown that increasing attraction interaction stabilizes the smectic phase at the cost of nematic phase leaving all other liquid crystalline transitions unchanged. Furthermore, the fluorescent dye molecules on the viral tips enable the observation of liquid crystalline lamellar structures with improved contrast and resolution. In situ visualization of topological defects in the smectic phase such as edge and screw dislocations has been thus performed at the lattice periodicity level. The displacement field around an edge dislocation has been experimentally established and compared to the profile predicted by elastic theory. Screw dislocations have been also evidenced, for which the core size and handedness have been determined.Dynamics of patchy and pristine viruses has been investigated by tracking individual rod displacements. In all liquid crystalline phases, the self-diffusion of patchy rods has been found to be hindered compared to the self-diffusion of pristine rods. Particularly in the smectic phase, patchy rods tend to reside within the layers mainly diffusing in the direction perpendicular to the main virus axis, contrary to pristine rods whose self-diffusion between layers is far more pronounced. This behavior is explained by the higher unidimensional smectic ordering potential experimentally measured in the dispersions of patchy rods compared to that obtained for pristine rods.We have combined both entropic and enthalpic patchinesses by adding non-adsorbing polymers into tip-functionalized viral dispersions. In this case, rod sides act as entropic patchy sites due to attractive depletion interaction between them. Small angle X-ray scattering and optical microscopy techniques have been used to compare the structural and dynamical properties of pristine and tip-functionalized viral dispersions mixed with hydrophilic polymers acting as depletants agent. We have determined and compared the phase diagrams obtained for the two types of virus-polymer systems.In summary, we have demonstrated a new and efficient way to control the structure of complex fluids by implementing site-specific modifications of building blocks
Structure et dynamique des colloĂŻdes en forme de bĂątonnets avec une interaction attractive directionnelle
Dispersions of filamentous viruses exhibit a plethora of liquid crystalline states including nematic, smectic (or lamellar), and columnar phases. Self-organization of these rod-shaped colloidal particles has been shown to map the hard-core behavior for which the interaction potential is purely repulsive. In this thesis, the structural and dynamical properties of rods with highly localized directional attractive interaction (or âpatchinessâ) between one of the ends of the particles have been studied. Local attraction has been achieved by functionalizing the filamentous virus tips via regioselective grafting hydrophobic fluorescent dyes which act as enthalpic patch. The single tip attraction strength can be tuned by varying the number of bound dye molecules. We have shown that increasing attraction interaction stabilizes the smectic phase at the cost of nematic phase leaving all other liquid crystalline transitions unchanged. Furthermore, the fluorescent dye molecules on the viral tips enable the observation of liquid crystalline lamellar structures with improved contrast and resolution. In situ visualization of topological defects in the smectic phase such as edge and screw dislocations has been thus performed at the lattice periodicity level. The displacement field around an edge dislocation has been experimentally established and compared to the profile predicted by elastic theory. Screw dislocations have been also evidenced, for which the core size and handedness have been determined.Dynamics of patchy and pristine viruses has been investigated by tracking individual rod displacements. In all liquid crystalline phases, the self-diffusion of patchy rods has been found to be hindered compared to the self-diffusion of pristine rods. Particularly in the smectic phase, patchy rods tend to reside within the layers mainly diffusing in the direction perpendicular to the main virus axis, contrary to pristine rods whose self-diffusion between layers is far more pronounced. This behavior is explained by the higher unidimensional smectic ordering potential experimentally measured in the dispersions of patchy rods compared to that obtained for pristine rods.We have combined both entropic and enthalpic patchinesses by adding non-adsorbing polymers into tip-functionalized viral dispersions. In this case, rod sides act as entropic patchy sites due to attractive depletion interaction between them. Small angle X-ray scattering and optical microscopy techniques have been used to compare the structural and dynamical properties of pristine and tip-functionalized viral dispersions mixed with hydrophilic polymers acting as depletants agent. We have determined and compared the phase diagrams obtained for the two types of virus-polymer systems.In summary, we have demonstrated a new and efficient way to control the structure of complex fluids by implementing site-specific modifications of building blocks.Les dispersions de virus filamenteux prĂ©sentent une succession d'Ă©tats cristallins liquides comprenant les phases nĂ©matique, smectique (ou lamellaire) et colonnaire. Lâauto-organisation de ces particules colloĂŻdales en forme de bĂątonnet sâest rĂ©vĂ©lĂ©e ĂȘtre essentiellement pilotĂ©e par lâentropie dont rĂ©sulte un potentiel dâinteraction entre particules purement rĂ©pulsif. Dans cette thĂšse, les propriĂ©tĂ©s structurales et dynamiques de bĂątonnets prĂ©sentant une interaction attractive directionnelle fortement localisĂ©e (interaction dite à « patch ») Ă l'une des extrĂ©mitĂ©s des particules ont Ă©tĂ© Ă©tudiĂ©es. Lâinteraction attractive locale a Ă©tĂ© obtenue en fonctionnalisant les extrĂ©mitĂ©s des virus filamenteux par greffage rĂ©giosĂ©lectif de colorants fluorescents hydrophobes qui jouent le rĂŽle de « patch » enthalpique. La force d'attraction peut ĂȘtre modulĂ©e en faisant varier le nombre de molĂ©cules de colorant liĂ©es. Nous avons montrĂ© que cette interaction à « patch » stabilise la phase smectique au dĂ©triment de la phase nĂ©matique, laissant les autres phases cristallines liquides essentiellement inchangĂ©es. En outre, la prĂ©sence de molĂ©cules de colorant fluorescent sur les extrĂ©mitĂ©s des virus permet l'observation de structures lamellaires cristal-liquides avec un contraste et une rĂ©solution exacerbĂ©s. La visualisation in situ de dĂ©fauts topologiques en phase smectique, telle des dislocations de type coin et vis, a Ă©tĂ© rĂ©alisĂ©e Ă l'Ă©chelle de la pĂ©riodicitĂ© du rĂ©seau. Le champ de dĂ©placement autour dâune dislocation coin a Ă©tĂ© Ă©tabli expĂ©rimentalement et comparĂ© au profil prĂ©dit par les thĂ©ories Ă©lastiques. Des dislocations de type vis ont Ă©galement Ă©tĂ© mises en Ă©vidence, pour lesquelles la taille du cĆur et l'helicite ont Ă©tĂ© dĂ©terminĂ©es.La dynamique des virus « patchy » et de ceux non fonctionnalisĂ©s a Ă©tĂ© Ă©tudiĂ©e par suivi temporel du dĂ©placement des particules individuelles en microscopie de fluorescence. Dans toutes les phases cristallines liquides, la diffusion de particules « patchy » s'est avĂ©rĂ©e ĂȘtre entravĂ©e. En particulier dans la phase smectique, les bĂątonnets « patchy » ont tendance Ă rĂ©sider dans les couches diffusant principalement dans la direction perpendiculaire Ă l'axe principal du virus, tandis que les bĂątonnets non fonctionnalisĂ©s prĂ©sentent une diffusion entre couches beaucoup plus prononcĂ©e. Ce comportement peut sâexplique par la plus grande valeur du potentiel smectique associĂ© et mesurĂ© expĂ©rimentalement dans les deux types de dispersion.Nous avons combinĂ© des effets de « patch » entropique et enthalpique en ajoutant des polymĂšres non-absorbants Ă la dispersion virale fonctionnalisĂ©e. Dans ce cas, les bĂątonnets sâauto-assemblent latĂ©ralement par dĂ©plĂ©tion en des clusters. La diffusion de rayons X et la microscopie optique ont Ă©tĂ© utilisĂ©es pour comparer les propriĂ©tĂ©s structurales et dynamiques des dispersions virales fonctionnalisĂ©es - ou pas - mĂ©langĂ©es Ă des polymĂšres non absorbants, et pour Ă©tablir les diagrammes de phases correspondants.En rĂ©sumĂ©, nous avons dĂ©montrĂ© un nouveau moyen efficace de contrĂŽler la structure de fluides complexes par la modifications rĂ©gio-sĂ©lective des particules constituantes
Directing liquid crystalline self-organization of Rodlike particles through tunable attractive single tips
Dispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities
Directing liquid crystalline self-organization of rod-like particles through tunable attractive single tips
Dispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities
Directing liquid crystalline self-organization of Rodlike particles through tunable attractive single tips
\u3cp\u3eDispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities.\u3c/p\u3
Rod-Like Virus-Based Multiarm Colloidal Molecules
We
report on the construction of multiarm colloidal molecules by
tip-linking filamentous bacteriophages, functionalized either by biological
engineering or chemical conjugation. The affinity for streptavidin
of a genetically modified vector phage displaying Strep-tags fused
to one end of the viral particle is measured by determining the dissociation
constant, <i>K</i><sub>d</sub>. In order to improve both
the colloidal stability and the efficiency of the self-assembly process,
a biotinylation protocol having a chemical yield higher than 90% is
presented to regioselectively functionalize the cystein residues located
at one end of the bacteriophages. For both viral systems, a theoretical
comparison is performed by developing a quantitative model of the
self-assembly and interaction of the modified viruses with streptavidin
compounds, which accurately accounts for our experimental results.
Multiarm colloidal structures of different valencies are then produced
by conjugation of these tip-functionalized viruses with streptavidin
activated nanoparticles. We succeed to form stable virus-based colloidal
molecules, whose number of arms, called valency, is solely controlled
by tuning the molar excess. Thanks to a fluorescent labeling of the
viral arms, the dynamics of such systems is also presented in real
time by fluorescence microscopy
Directing liquid crystalline self-organization of rod-like particles through tunable attractive single tips
Dispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities