A cationic surfactant containing a spiropyran unit is prepared exhibiting a dual‐responsive adjustability of its surface‐active characteristics. The switching mechanism of the system relies on the reversible conversion of the non‐ionic spiropyran (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH‐dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli‐responsive behavior enables remote‐control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH‐dependent manipulation of oil‐in‐water emulsions.
We present a microcontact
printing (μCP) routine suitable
to introduce defined (sub-) microscale patterns on surface substrates
exhibiting a high capillary activity and receptive to a silane-based
chemistry. This is achieved by transferring functional trivalent alkoxysilanes,
such as (3-aminopropyl)-triethoxysilane (APTES) as a low-molecular
weight ink via reversible covalent attachment to polymer brushes grafted
from elastomeric polydimethylsiloxane (PDMS) stamps. The brushes consist
of poly{
N
-[tris(hydroxymethyl)-methyl]acrylamide}
(PTrisAAm) synthesized by reversible addition–fragmentation
chain-transfer (RAFT)-polymerization and used for immobilization of
the alkoxysilane-based ink by substituting the alkoxy moieties with
polymer-bound hydroxyl groups. Upon physical contact of the silane-carrying
polymers with surfaces, the conjugated silane transfers to the substrate,
thus completely suppressing ink-flow and, in turn, maximizing printing
accuracy even for otherwise not addressable substrate topographies.
We provide a concisely conducted investigation on polymer brush formation
using atomic force microscopy (AFM) and ellipsometry as well as ink
immobilization utilizing two-dimensional proton nuclear Overhauser
enhancement spectroscopy (
1
H–
1
H-NOESY-NMR).
We analyze the μCP process by printing onto Si-wafers and show
how even distinctively rough surfaces can be addressed, which otherwise
represent particularly challenging substrates.
Ein kationisches Tensid mit einer Spiropyran‐Einheit wurde hergestellt, dessen oberflächenaktives Verhalten in dual‐responsiver Weise einstellbar ist. Der Schaltmechanismus des Tensids beruht auf der umkehrbaren Umwandlung des nichtionischen Spiropyrans (SP) zu einer ionischen Merocyaninform (MC/H+), die über eine Änderung des pH‐Wertes der Lösung oder durch Einstrahlung von Licht mit passender Wellenlänge ausgelöst werden kann. Das entsprechende pH‐abhängige photoaktive Verhalten lässt sich so zusammenfassen, dass im Sauren ein ausgeprägter Unterschied zwischen der Oberflächenaktivität beider Formen des Tensids besteht, während dieses Verhalten im neutralen pH‐Bereich unterdrückt ist. Die zugrundeliegenden Prozesse werden vertieft untersucht und eine thermodynamische Erklärung, der eine Verknüpfung aus theoretischen Betrachtungen und experimentellen Ergebnissen zu Grunde liegt, wird gegeben. Das komplexe stimuli‐responsive Verhalten ermöglicht einen gesteuerten Eingriff in kolloidale Systeme. Mithin wird der pH‐abhängige Manipulation einer durch das Tensid stabilisierten Öl‐in‐Wasser‐Emulsion gezeigt, die die vorliegende Studie um eine Anwendung ergänzt.
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