| 1. |
- Campbell, Richard A., et al.
(författare)
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Direct Impact of Nonequilibrium Aggregates on the Structure and Morphology of Pdadmac/SDS Layers at the Air/Water Interface
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:29, s. 8664-8674
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Tidskriftsartikel (refereegranskat)abstract
- We discuss different nonequilibrium mechanisms by which bulk aggregates directly modify, and can even control, the interfacial structure and morphology of an oppositely charged polyelectrolyte/surfactant (P/S) mixture. Samples are categorized at the air/water interface with respect to the dynamic changes in the bulk phase behavior, the bulk composition, and the sample history using complementary surface-sensitive techniques. First, we show that bulk aggregates can spontaneously interact with the adsorption layer and are retained in it and that this process occurs most readily for positively charged aggregates with an expanded structure. In this case, key nonequilibrium issues of aggregate dissociation and spreading of surface-active material at the interface have a marked influence on the macroscopic interfacial properties. In a second distinct mechanism, aggregates inherently become trapped at the interface during its creation and lateral flocculation occurs. This irreversible process is most pronounced for aggregates with the lowest charge. A third mechanism involves the deposition of aggregates at interfaces due to their transport under gravity. The specificity of this process at an interface depends on its location and is mediated by density effects in the bulk. The prevalence of each mechanism critically depends on a number of different factors, which are outlined systematically here for the first time. This study highlights the sheer complexity by which aggregates can directly impact the interfacial properties of a P/S mixture. Our findings offer scope for understanding seemingly mysterious irreproducible effects which can compromise the performance of formulations in wide-ranging applications from foams to emulsions and lubricants.
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| 2. |
- Campbell, Richard A., et al.
(författare)
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Effects of Bulk Colloidal Stability on Adsorption Layers of Poly(diallyldimethylammonium Chloride)/Sodium Dodecyl Sulfate at the Air-Water Interface Studied by Neutron Reflectometry
- 2011
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:51, s. 15202-15213
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Tidskriftsartikel (refereegranskat)abstract
- We show for the oppositely charged system poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate that the cliff edge peak in its surface tension isotherm results from the comprehensive precipitation of bulk complexes into sediment, leaving a supernatant that is virtually transparent and a depleted adsorption layer at the air/water interface. The aggregation and settling processes take about 3 days to reach completion and occur at bulk compositions around charge neutrality of the complexes which lack long-term colloidal stability. We demonstrate excellent quantitative agreement between the measured surface tension values and a peak calculated from the surface excess of surfactant in the precipitation region measured by neutron reflectometry, using the approximation that there is no polymer left in the liquid phase. The nonequilibrium nature of the system is emphasized by the production of very different interfacial properties from equivalent aged samples that are handled differently. We go on to outline our perspective on the "true equilibrium" state of this intriguing system and conclude with a comment on its practical relevance given that the interfacial properties can be so readily influenced by the handling of kinetically trapped bulk aggregates.
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| 3. |
- Campbell, Richard A., et al.
(författare)
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Multilayers at Interfaces of an Oppositely Charged Polyelectrolyte/Surfactant System Resulting from the Transport of Bulk Aggregates under Gravity
- 2012
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 116:27, s. 7981-7990
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Tidskriftsartikel (refereegranskat)abstract
- We show conclusively that multilayers at interfaces of an oppositely charged polyelectrolyte/surfactant system can result from the transport under gravity of bulk aggregates with internal molecular structure. This process was demonstrated by measurements of poly-(diallyldimethylammonium chloride)/sodium dodecyl sulfate solutions at the air/liquid and solid/liquid interfaces using neutron reflectometry. In the latter case a novel approach involving the comparison of reflection up versus down measurements provided key evidence. Interfacial multilayers indicated by a strong Bragg peak and clear off-specular scattering are exhibited under three conditions: (1) only for samples in the phase separation region, (2) only for fresh samples where a suspension of bulk aggregates remains in solution, and (3) only when the creaming or sedimentation process occurs in the direction of the interface under examination. This bulk transport mechanism is an alternative route of formation of interfacial multilayers to surface induced self assembly The two processes evidently give rise to interfaces with very different structural and rheological properties. Such directionality effects in the formation of nanostructured liquid interfaces may have implications for a broad range of soft matter and biophysical systems containing macromolecules such as synthetic polymers, proteins, or DNA.
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| 4. |
- Campbell, Richard A., et al.
(författare)
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New Perspective on the Cliff Edge Peak in the Surface Tension of Oppositely Charged Polyelectrolyte/Surfactant Mixtures
- 2010
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:20, s. 3021-3026
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Tidskriftsartikel (refereegranskat)abstract
- We present how dramatically the nonequilibrium nature of an oppsitely charged polyelectrolyte/surfactant mixture can affect the interfacial properties. We show for the first time that the cliff edge peak in the surface tension of the poly(diallydimethylammonium chloride)/sodium dodecyl surfate system is produced as a direct result of depletion of surface-active material from the bulk solution due to a show precipitation process in the phase separation region. Simple illustrations are given of how to control the production of the peak, to eliminate the feature for equivalent aged solutions through the use of different sample handling methods, and even to change its characteristics at short surface ages. The potential to tune nonequilibrium, steady-state interfacial properties for such strongly associating system is clearly demonstrated. We propose that our findings in general may be applicable to a broad range of mixture containing surfactants and oppositely charged macromolecules such as polymers proteins and DNA.
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| 5. |
- Michanek, Agnes, et al.
(författare)
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RNA and DNA Association to Zwitterionic and Charged Monolayers at the Air-Liquid Interface
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:25, s. 9621-9633
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to establish under which conditions short RNA molecules (similar to miRNA) associate with zwitterionic phospholipids and how this differs from the association with cationic surfactants. We study how the base pairing (i.e., single stranded versus double stranded nucleic acids) and the length of the nucleic acid and the charge of the lipid/surfactant monolayer affect the association behavior. For this purpose, we study the adsorption of nucleic acids to monolayers composed of dipalmitoyl phosphatidylcholine (DPPC) or dioctadecyl-dimethyl-ammoniumbromide (DODAB) using the surface film balance, neutron reflectometry, and fluorescence microscopy. The monolayer studies with the surface film balance suggested that short single-stranded ssRNA associates with liquid expanded zwitterionic phospholipid monolayers, whereas less or no association is detected for double-stranded dsRNA and dsDNA In order to quantify the interaction and to determine the location of the nucleic acid in the lipid/surfactant monolayer we performed neutron reflectometry measurements. It was shown that ssRNA adsorbs to and penetrates the liquid expanded monolayers, whereas there is no penetration of nucleic acids into the liquid condensed monolayer. No adsorption was detected for dsDNA to zwitterionic monolayers. On the basis of these results, we propose that the association is driven by the hydrophobic interactions between the exposed hydrophobic bases of the ssRNA and the hydrocarbon chains of the phospholipids. The addition of ssRNA also influences domain formation in the DPPC monolayer, leading to fractal-like interconnected domains. The experimental results are discussed in terms of the implication for biological processes and new leads for applications in medicine and biotechnology.
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| 6. |
- Yanez, Marianna, et al.
(författare)
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Adsorption of Mixtures of Poly(amidoamine) Dendrimers and Sodium Dodecyl Sulfate at the Air-Water Interface.
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:20, s. 5817-5828
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Tidskriftsartikel (refereegranskat)abstract
- We relate the adsorption from mixtures of well-defined poly(amidoamine) (PAMAM) dendrimers of generations 4 and 8 with sodium dodecyl sulfate (SDS) at the air-water interface to the bulk solution properties. The anionic surfactant shows strong attractive interactions with the cationic dendrimers at pH 7, and electrophoretic mobility measurements indicate that the association is primarily driven by electrostatic interactions. Optical density measurements highlight the lack of colloidal stability of the formed bulk aggregates at compositions close to charge neutrality, the time scale of which is dependent on the dendrimer generation. Adsorption at the air-water interface was followed from samples immediately after mixing using a combination of surface tension, neutron reflectometry, and ellipsometry measurements. In the phase separation region for dendrimers of generation 4, we observed high surface tension corresponding to a depleted surfactant solution but only when the aggregates carried an excess of surfactant. Interestingly, these depleted adsorption layers contained spontaneously adsorbed macroscopic aggregates, and these embedded particles do not rearrange to spread monomeric material at the interface. These findings are discussed in relation to the interfacial properties of mixtures involving dendrimers of generation 8 as well as polydisperse linear and hyperbranched polyelectrolytes where there is polyelectrolyte bound to a surfactant monolayer. The results presented here demonstrate the capability of dendrimers to sequester anionic surfactants in a controllable manner, with potential applications as demulsification and antifoaming agents.
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| 7. |
- Yanez, Marianna, et al.
(författare)
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Interactions of PAMAM Dendrimers with Negatively Charged Model Biomembranes.
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:45, s. 12892-12906
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the interactions between cationic poly(amidoamine) (PAMAM) dendrimers of generation 4 (G4), a potential gene transfection vector, with net-anionic model biomembranes composed of different ratios of zwitterionic phosphocholine (PC) and anionic phospho-l-serine (PS) phospholipids. Two types of model membranes were used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl (PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers, formed at the interface between two aqueous droplets in oil (droplet interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers were found to translocate through POPC:POPS bilayers deposited on silica surfaces. The charge density of the bilayer affects translocation, which is reduced when the ionic strength increases. This shows that the dendrimer-bilayer interactions are largely controlled by their electrostatic attraction. The structure of the solid-supported bilayers remains intact upon translocation of the dendrimer. However, the amount of lipids in the bilayer decreases and dendrimer/lipid aggregates are formed in bulk solution, which can be deposited on the interfacial layers upon dilution of the system with dendrimer-free solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers cross the lipid membranes containing PS, which then become more permeable to ions. The obtained results have implications for PAMAM dendrimers as delivery vehicles to cells.
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| 8. |
- Yanez, Marianna, et al.
(författare)
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Interactions of PAMAM Dendrimers with SDS at the Solid-Liquid Interface
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:19, s. 5817-5831
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Tidskriftsartikel (refereegranskat)abstract
- This work addresses structural and nonequilibrium effects of the interactions between well-defined cationic poly(amidoamine) PAMAM dendrimers of generations 4 and 8 and the anionic surfactant sodium dodecyl sulfate (SDS) at the hydrophilic silica-water interface. Neutron reflectometry and quartz crystal microbalance with dissipation monitoring were used to reveal the adsorption from premixed dendrimer/surfactant solutions as well as sequential addition of the surfactant to preadsorbed layers of dendrimers. PAMAM dendrimers of both generations adsorb to hydrophilic silica as a compact monolayer, and the adsorption is irreversible upon rinsing with salt solution. SDS adsorbs on the dendrimer layer and at low bulk concentrations causes the expansion of the dendrimer layers on the surface. When the bulk concentration of SDS is increased, the surfactant layer consists of aggregates or bilayer-like structures The adsorption of surfactant is reversible upon rinsing, but slight changes of the structure of the preadsorbed PAMAM monolayer were observed The adsorption from premixed solutions close to charge neutrality results in thick multilayers, but the surface excess is lower when the bulk complexes have a net negative charge. A critical examination of the pathway of adsorption for the interactions of SDS with preadsorbed PAMAM monolayers and premixed PAMAM/SDS solutions with hydrophilic silica revealed that nonequilibrium effects are important only in the latter case, and the application of a thermodynamic model to such experimental data would be inappropriate.
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| 9. |
- Yanez, Marianna, et al.
(författare)
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Interactions of Small Dendrimers with Sodium Dodecyl Sulfate at the Air-Water Interface.
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:40, s. 11835-11848
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Tidskriftsartikel (refereegranskat)abstract
- We have determined how the bulk behavior of mixtures of small cationic poly(amidoamine) dendrimers (generation 2, PAMAM-G2) and sodium dodecyl sulfate (SDS) affects the structure and composition of the adsorbed layers at the air-water interface. The aim is to reveal how the size of a well-defined hyperbranched polyelectrolyte affects the interfacial and bulk solution behavior of mixtures with oppositely charged surfactants, when the size of the polyelectrolyte approaches that of the surfactant. A combination of electrophoretic mobility, UV-vis spectroscopy, dynamic light scattering, and small-angle X-ray scattering measurements have been employed to characterize the interactions in the bulk solution. PAMAM-G2 associates strongly with SDS in the bulk, forming large aggregates where the size and the charge depend on the bulk composition. We show that kinetically trapped aggregates can be formed at compositions outside the equilibrium two-phase region, and the positively charged aggregates are larger than the negative ones. Surface tensiometry, neutron reflectometry, and ellipsometry have been used to reveal the properties of the interfacial layers. The interfacial structures formed depend strongly on the bulk composition: structured layers are present for samples inside the two-phase region, whereas intact nanostructured aggregates adsorb for samples just outside the two-phase region. The interfacial behavior of PAMAM-G2/SDS mixtures is compared with that of small amines or multivalent ions and oppositely charged surfactants. The implications of aggregate adsorption, dissociation, and spreading processes are discussed as well as the potential of small dendrimers for applications involving the delivery of functional molecules to interfaces.
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| 10. |
- Yanez, Marianna, et al.
(författare)
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Molecular recognition of nucleic acids by nucleolipid/dendrimer surface complexes.
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 10:42, s. 8401-8405
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Tidskriftsartikel (refereegranskat)abstract
- We show for the first time that 1,2-dilauroyl-sn-glycero-3-phosphatidyladenosine nucleolipid surface complexes with cationic poly(amidoamine) dendrimers can be used to selectively bind DNA including oligonucleotides. This molecular recognition has high potential for applications involving biomedical and bioanalytic devices as well as drug delivery systems based on nucleic acids.
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| 11. |
- Yanez, Marianna
(författare)
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Nanostructured surfaces created by the interactions of dendrimers and oppositely charged amphiphiles
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research described in this thesis aims to understand the interactions between cationic poly(amidoamine) (PAMAM) dendrimers and small oppositely charged amphiphiles at the solid-liquid and air-liquid interfaces in relation to the bulk solution behavior. There is high interest in PAMAM dendrimers because they are well-defined polymers with a hierarchical architecture which makes them promising materials as nanocapsules and gene vectors. In the first part of the work, the bulk solution and interfacial properties of mixtures of PAMAM dendrimers of generations 2, 4 and 8 and the anionic surfactant sodium dodecyl sulfate (SDS) were studied. At the solid-liquid interface, the structure and composition of the adsorbed layers depend on the dendrimer generation, the bulk composition and the pathway of adsorption. At the air-water interface, there is a synergistic enhancement of adsorbed surfactant in the presence of PAMAM dendrimers and the interfacial behavior depends on the non-equilibrium properties of the aggregates formed in the bulk solution. The implications of the interfacial properties of the layers formed by PAMAM/SDS mixtures are discussed with respect to their possible applications. The interactions of PAMAM dendrimers and negatively charged lipid bilayers were also investigated. The aim was to understand the transport mechanism of dendrimers across anionic model biomembranes. The addition of PAMAM dendrimers of generation 4 to solid supported and droplet interface bilayers showed that the dendrimer makes the membranes more permeable and this allows them to translocate through the membranes. The results are employed to evaluate the use of PAMAM dendrimers as delivery vehicles. The last section is dedicated to the examination of the interactions between PAMAM dendrimers of generation 4 and the nucleolipids dilauroylphospholiponucleosides based on adenosine (DLPA) and uridine (DLPU) at the silica-water interface. The aim was to develop ‘smart’ complexes on surfaces to achieve selective binding of nucleic acids. The layer structure and functionality depend on the method of adsorption and the type of nucleolipid. Only PAMAM/DLPA layers showed selective hydrophobic and hydrogen bonding base pairing interactions with different strands of nucleic acids through the formation of nucleolipid/nucleic acid multilayers.
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