Patent Publication Number: US-2023157358-A1

Title: Diffusion Barrier

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the first application for the instant invention. 
     TECHNICAL FIELD 
     This application relates generally to a pod for storing atomizable liquid for use in a vaporizer system, and more particularly to a vaping system pod having a diffusion barrier to prevent migration of flavors for use in conjunction with an electronic cigarette or vaporizer. 
     BACKGROUND 
     Electronic cigarettes and vaporizers are well regarded tools in smoking cessation. In some instances, these devices are also referred to as an electronic nicotine delivery system (ENDS). A nicotine based liquid solution, commonly referred to as e-liquid, often paired with a flavoring, is atomized in the ENDS for inhalation by a user. In some embodiments, e-liquid is stored in a cartridge or pod, which is a removable assembly having a reservoir from which the e-liquid is drawn towards a heating element by capillary action through a wick. In many such ENDS, the pod is removable, disposable, and is sold pre-filled. 
     In some ENDS, a refillable tank is provided, and a user can purchase a vaporizable solution with which to fill the tank. This refillable tank is often not removable, and is not intended for replacement. A fillable tank allows the user to control the fill level as desired. Disposable pods are typically designed to carry a fixed amount of vaporizable liquid, and are intended for disposal after consumption of the e-liquid. The ENDS cartridges, unlike the aforementioned tanks, are not typically designed to be refilled. Each cartridge stores a predefined quantity of e-liquid, often in the range of 0.5 to 3 ml. In ENDS systems, the e-liquid is typically composed of a combination of any of vegetable glycerine, propylene glycol, nicotine and flavorings. In systems designed for the delivery of other compounds, different compositions may be used. In some systems, a carrier solution (which may be composed of at least one of vegetable glycerine and propylene glycol) is used to carry cannabinoids and optionally terpenes. 
     In the manufacturing of the disposable cartridge, different techniques are used for different cartridge designs. Typically, the cartridge has a wick that allows e-liquid to be drawn from the e-liquid reservoir to an atomization chamber. In the atomization chamber, a heating element in communication with the wick is heated to encourage aerosolization of the e-liquid. The aerosolized e-liquid can be drawn through a defined air flow passage towards a user’s mouth. 
       FIGS.  1 A,  1 B and  1 C  provide front, side and bottom views of an exemplary pod  50 . Pod  50  is composed of a reservoir  52  having an air flow passage  54 , and an end cap assembly  56  that is used to seal an open end of the reservoir  52 . End cap assembly has wick feed lines  58  which allow e-liquid stored in reservoir  52  to be provided to a wick (not shown in  FIG.  1   ). To ensure that e-liquid stored in reservoir  52  stays in the reservoir and does not seep or leak out, and to ensure that end cap assembly  56  remains in place after assembly, seals  60  can be used to ensure a more secure seating of the end cap assembly  56  in the reservoir  52 . In the illustrated embodiment, seals  60  may be implemented through the use of o-rings. 
     As noted above, pod  50  includes a wick that is heated to atomize the e-liquid. To provide power to the wick heater, electrical contacts  62  are placed at the bottom of the pod  50 . In the illustrated embodiment, the electrical contacts  62  are illustrated as circular. The particular shape of the electrical contacts  62  should be understood to not necessarily germane to the function of the pod  50 . 
     Because an ENDS device is intended to allow a user to draw or inhale as part of the nicotine delivery path, an air inlet  64  is provided on the bottom of pod  50 . Air inlet  64  allows air to flow into a pre-wick air path through end cap assembly  56 . The air flow path extends through an atomization chamber and then through post wick air flow passage  54 . 
     A mouthpiece  68  is illustrated in section sitting atop pod  50 , with an absorbent pad  66  between the two. Absorbent pad  66  facilitates the absorption of large droplets and of any condensation of e-liquid that occurs during and after the use of the pod  50 . The mouthpiece has apertures to allow the airflow through the pod to be delivered to the user. By selecting a location for the apertures, a curve can be introduced into the airflow, which may discourage the delivery of large droplets that are often associated with spitback. 
       FIG.  2    illustrates a cross section taken along line A in  FIG.  1 B . This cross section of the device is shown with a complete (non-sectioned) wick  66  and heater  68 . End cap assembly  56  resiliently mounts to an end of air flow passage  54  in a manner that allows air inlet  64  to form a complete air path through pod  50 . This connection allows airflow from air inlet  64  to connect to the post air flow path through passage  54  through atomization chamber  70 . Within atomization chamber  70  is both wick  66  and heater  68 . When power is applied to contacts  62 , the temperature of the heater increases and allows for the volatilization of e-liquid that is drawn across wick  66 . 
     Typically the heater  68  reaches temperatures well in excess of the vaporization temperature of the e-liquid. This allows for the rapid creation of a vapor bubble next to the heater  68 . As power continues to be applied the vapor bubble increases in size, and reduces the thickness of the bubble wall. At the point at which the vapor pressure exceeds the surface tension the bubble will burst and release a mix of the vapor and the e-liquid that formed the wall of the bubble. The e-liquid is released in the form of aerosolized particles and droplets of varying sizes. These particles are drawn into the air flow and into post wick air flow passage  54  and towards the user. 
       FIG.  3    illustrates an alternate embodiment of pod  50 , shown in cross section. Pod  50  is comprised of a reservoir  52  having a post-wick air passage  54 . An end cap  56  is inserted into the bottom end of the reservoir  52  to seal the pod  50 , typically after filling the reservoir  52  with e-liquid. The end cap  56  has wick feed lines  58  to allow e-liquid from the reservoir  52  to enter the end cap  56  to make contact with wick  72 . Electrical leads  62  allow power to be provided to pod  50  and generate heat in heater  74 . As with the earlier described embodiments, this generates bubbles within the e-liquid atop the heater  74 .When a bubble reaches a size determined by a number of physical characteristics, it will rupture. These characteristics include a number of properties of the e-liquid, but effectively a bubble will rupture when the surface tension of the e-liquid (forming the bubble) is no longer sufficient to overcome the increasing vapor pressure inside the bubble. This rupturing of the bubble will result in the release of a quantity of e-liquid, as well as e-liquid droplets of varying sizes from what was the surface of the bubble. Because in most vaping devices, the application of power to heater  74  is tied to the user drawing on the vaping device, the vapor and droplets are entrained within an airflow through pre-wick airflow passage  64 , into atomization chamber  70  and out through post wick airflow passage  54 . 
     This illustrated embodiment differs from the previously illustrated embodiment in that in place of using O-rings as seals, a resilient cap  76  is employed. This resilient cap may be made of a material such as silicone that can deform under pressure, but will typically return to its original shape. Resilient cap  76  is sized to fit atop end cap  56 , so that when inserted into reservoir  52 , the resilient cap  76  will be deformed, and will provide a seal to mitigate leakage of e-liquid. The resilient cap  76  is also used in this illustrated embodiment to provide an airflow feature  78  into a post-wick airflow path. In other embodiments, the airflow feature could be integrated into the post-wick airflow path  54  for a similar, or the same, effect. A blunt airflow feature allows the e-liquid laden airflow to be interrupted and for vortices to be introduced into the airflow within the post wick airflow passage  54 . These vortices can encourage larger droplets within the airflow to be pushed into or towards the sidewalls of post wick airflow passage  54 , which can act to remove droplets associated with spitback or other undesirable phenomena from the e-liquid laden airflow. 
     As noted above, the e-liquid is delivered to the user in two forms: a vapor caused by the heating of e-liquid, and droplets of varying sizes caused by the vapor rupturing the surface of the bubble. The e-liquid is a solution of a number of different components, each of which can have its own specific vaporization temperature. Typically the temperature of the heater is set to allow for vaporization of a component such as the propylene glycol as it represents the largest fraction of the e-liquid. This allows for the vaporization to occur quickly, and results in good droplet production. Some of the components may be either dissolved in the e-liquid solution or carried in suspension within the e-liquid solution. These components may not evaporate at the heater when the e-liquid itself is volatilized. As a result, the portion of the e-liquid that is turned to a vapour is likely to leave behind a precipitate. This precipitate is often a flavorant or a compound used to provide a sweetness to the vaping experience. The resultant precipitate will accumulate at the site of the evaporation. 
     As the number of heating cycles increases, the amount of precipitate that is left behind increases. It has been observed that some vaping systems will accumulate a residue that becomes darker over time. It is believed that this residue may be a result of the burning of this precipitate. The heating of the precipitate may result in more than an aesthetically unpleasant buildup residue. The residue itself is subjected to the heating cycle intended to vaporize e-liquid, which often involves temperatures in excess of 200° C. This may result in either a “caramelization” of the sugars and sugar substitutes. It should be understood that this residue may burn without burning the substrate of the wick  72 . This creates two different pathways for combustion that would result in a so-called burnt hit, the first being combustion involving material within the wick  72 , such as cotton, and the second being the burning of the residue. It may also be possible for both of these to burn together, but it is not believed to be a requirement for them to burn together. 
     It should be understood that the wick  72  is in fluid communication with the e-liquid stored within the reservoir  52 . As a result, when the e-liquid within the wick  72  is replenished, the residue discussed above can migrate through the wick  72  and may then contaminate the e-liquid within reservoir  52 . This contamination may result in discoloration of the e-liquid within the reservoir  52 , and in some cases it may result in a change in the flavor of the e-liquid. This is an undesirable effect that is often based on the manner in which the e-liquid is consumed, the design of the pod, the rate of e-liquid consumption and many other factors. As a result of the number of factors associated with this contamination, it is a difficult process to prevent, and it may only intermittently affect some users. 
     This contamination effect can result in users becoming concerned or upset about the quality of the e-liquid or the vaping system itself. It would therefore be beneficial to have a mechanism to prevent the migration of residue from the wick into the e-liquid within the reservoir. 
     SUMMARY 
     It is an object of the aspects of the present invention to obviate or mitigate the problems of the above-discussed prior art. 
     Through the use of a barrier between the wick and the reservoir, migration of residue from the atomization of liquids from the wick into the reservoir is impeded. This barrier can perform any of a number of functions including slowing the movement of e-liquid carrying the residue, filtering residue from e-liquid migrating through the barrier, and preventing movement of e-liquid in one direction. In this way, the barrier can prevent the fouling of the e-liquid within the reservoir which may cause at least one of flavor changes to e-liquid within the reservoir and visual changes to the color of the stored e-liquid. 
     In a first aspect of the present invention, there is provided a pod for storing atomizable liquid. This pod is designed for use within a vaping system and comprises a reservoir, a heater, a wick, and a diffusion barrier. The reservoir is used to store the atomizable liquid. The wick is in fluid communication with the atomizable liquid stored within the reservoir and draws the atomizable liquid from the reservoir towards the heater, which can be used to atomize the atomizable liquid. The diffusion barrier, in some embodiments, is distinct from the wick, and is interposed between the wick and the reservoir. The barrier can resist or impede migration of residue resulting from atomization of the atomizable liquid from the wick into the atomizable liquid within the reservoir. 
     In an embodiment of the first aspect of the present invention, the atomizable liquid is an e-liquid comprising at least one of vegetable glycerine, propylene glycol, nicotine and a flavorant. In another embodiment, the atomizable liquid comprises a cannabinoid. 
     In another embodiment, the heater is aligned with an airflow path through the pod to allow atomized liquid to be entrained in an airflow in the airflow path. In some embodiments, the diffusion barrier is a sponge comprising spun nylon, and is optionally in physical contact with first and second ends of the wick and in some embodiments it may occlude a wick feed line between the reservoir and the wick. In some embodiments, the diffusion barrier does not contact the wick, and may optionally occlude a wick feed line between the reservoir and the wick. 
     In another embodiment, the diffusion barrier is situated in the reservoir, and optionally may be a membrane such as a semi permeable membrane. The membrane may comprise expanded polytetrafluoroethylene. It should be understood that reference to a semi permeable membrane should also be understood to mean that the membrane allows e-liquid to travel through the membrane in one direction but not in the other. In further embodiments, the membrane allows movement of the e-liquid in both directions, but that there is a directional preference so that the e-liquid can move more freely in one direction than the other. 
     In a further embodiment, the barrier is a spun nylon sponge. In another embodiment, the barrier is comprised of at least one of cotton, nylon, wool, linen, and hemp. In some embodiments, the wick is vertically aligned within the pod around an airflow path through the pod. Optionally the diffusion barrier forms a ring around the wick, and the diffusion barrier may isolate the wick from the reservoir. 
     In a second aspect of the present invention, there is provided a vaporizer system for atomizing an atomizable liquid. The vaporizer systems comprises a battery, a reservoir, a heater, control circuitry, a wick and a diffusion barrier. The battery is used for storing power. The reservoir is used for storing the atomizable liquid. The heater is used to atomize the atomizable liquid in response to receipt of power from the battery. The control circuitry can be used to control the application of from the battery to the heater in response to an indication of use. The wick draws atomizable liquid from the reservoir towards the heater. The diffusion barrier is distinct from the wick, and is interposed between the wick and the reservoir. The diffusion barrier impedes migration of residue resulting from atomization of the atomizable liquid from the wick into the atomizable liquid within the reservoir. 
     In some embodiments of the second aspect, the control circuitry is embodied within a processor that can execute stored instructions to carry out control of the application of power to the heater. 
     It should be understood that embodiments of the first aspect can be applied, with suitable modifications that would be apparent to those skilled in the art, to the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       Embodiments of the present invention will now be described in further detail by way of example only with reference to the accompanying figure in which: 
         FIG.  1 A  is a front view of a prior art pod for use in an electronic nicotine delivery system; 
         FIG.  1 B  is a side view of the pod of  FIG.  1 A ; 
         FIG.  1 C  is a bottom view of the pod of  FIG.  1 A ; 
         FIG.  2    is a cross section of the pod of  FIGS.  1 A and  1 B  along cut line A in  FIG.  1 B ; 
         FIG.  3    is a cross section view of an alternate embodiment of the pod illustrated in  FIGS.  1 A-C and  2   ; 
         FIG.  4    illustrates a cross section view of a pod according to a non-limiting embodiment of the present invention; 
         FIG.  5 A  illustrates a front cross section view of a pod according to an alternate non-limiting embodiment of the present invention; 
         FIG.  5 B  illustrates a side view cross section of a wick and diffusion barrier as illustrated in  FIG.  5 A ; 
         FIG.  6    illustrates a front cross section view of a pod according to an alternate non-limiting embodiment of the present invention; and 
         FIG.  7    illustrates a front cross section view of a pod according to an alternate non-limiting embodiment of the present invention; and 
         FIG.  8 A  illustrates a front view of a diffusion barrier wick according to an alternate non-limiting embodiment of the present invention;; 
         FIG.  8 B  illustrates a cross section of the wick of  FIG.  8 A  taken along section line 8B; and 
         FIG.  8 C  illustrates a cross section of the wick of  FIG.  8 B  taken along section line 8C. 
     
    
    
     DETAILED DESCRIPTION 
     In the instant description, and in the accompanying figures, reference to dimensions may be made. These dimensions are provided for the enablement of a single embodiment and should not be considered to be limiting or essential. Disclosure of numerical range should be understood to not be a reference to an absolute value unless otherwise indicated. Use of the terms about or substantively with regard to a number should be understood to be indicative of an acceptable variation of up to ±10% unless otherwise noted. 
     To address issues associated with the back migration of residue, left with the wick after atomizing e-liquid, through the wick and into the e-liquid within the reservoir, various embodiments described below will introduce a diffusion barrier that allows e-liquid to enter the wick, but resists the migration of the residue through the wick and into the e-liquid. It should be understood that a diffusion barrier may simply slow the back migration, as the contents of the reservoir are finite, and so long as the back migration is sufficiently slowed, the residue will not be provided an opportunity to foul the e-liquid before the e-liquid is consumed. Even if the pod in question is a refillable pod, there is a lifespan associated with the pod, so back propagation is only necessary for a finite time. 
     In some embodiments the diffusion barrier will be integrated within the wick to create a wick with directional capillary action, so that the capillary action of the wick draws e-liquid towards the center of the wick and resists the flow of e-liquid (and especially residue dissolved within the e-liquid) from the center of the wick outwards. 
       FIG.  4    is a cross-sectional view of a pod  100  that impedes back migration of residues from the wick into the reservoir. Pod  100  has a reservoir  102  which defines a post-wick airflow passage  104 . Reservoir  102  can be filled with e-liquids and then sealed through the insertion of end cap  106 . End cap  106  includes wick feed lines  108  that allow e-liquid from the reservoir  102  to be supplied to wick  116 . Power can be provided to pod  100  through electrical leads  110 , which are connected to heater  118  which engages with wick  116  so e-liquid saturating the wick  116  can be properly volatilized by the heating of heater  118 . Airflow through the pod  100  starts with pre-wick airflow passage  114 , proceeds to atomization chamber  114  where it passes over the heater  118  and wick  116 . Airflow then continues into post wick airflow passage  104 . End cap  106  forms a sealing engagement with the reservoir  102 , which in the illustrated embodiment is aided by the presence of resilient cap  120 , which can be made of a physically resilient material such as silicone. The resilient cap  120  can be fitted atop end cap  106  so that when inserted into reservoir  102 , the resilient cap is at least partially compressed, resulting in a sealing engagement designed to prevent egress of the e-liquid from any gaps between the end cap  106  and reservoir  102 . Within resilient cap  120 , an airflow feature  122  is introduced, so that the airflow passing over wick  116  and heater  118  impacts upon the feature  122 . This airflow feature, although shown as being implemented in resilient cap  120  may also be introduced into post wick airflow passage  104 . When an airflow passes over wick  116  and heater  118 , it entrains e-liquid in the form of droplets of varying sizes. Some of these droplets are of a size that is associated with poor user experiences. To avoid providing the user with droplets that are too large, airflow feature  122  creates turbulence in the post wick airflow, and may cause vortices to form. These vortices cause e-liquid droplets over a threshold size to be pushed into the walls of post wick airflow passage  104 , thus removing them from the airflow. 
     Diffusion barrier  124  is shown as having been inserted into the wick feed lines  108 . E-liquid from reservoir  102  can saturate diffusion barrier  124 , and then fill wick feed lines  108 , allowing wick  116  to draw e-liquid across itself through capillary action. Diffusion barrier  124  is, as discussed above, intended to slow or restrict the migration of at least some of the built-up residue, from wick  116  into the e-liquid within reservoir  102 . Residues may be associated with precipitate formed from the heating of e-liquid to a vapor state. The vapor from a nicotine based e-liquid is largely the carrier liquid, with additions such as flavorants and even possibly nicotine failing to vaporize. The flavorants and nicotine are delivered in the droplets associated with the rupture of the bubbles. As more e-liquid is drawn through wick  116 , the amount of precipitate left on or near the heaters increases. Due to the presence of flavorants and sweeteners, the precipitate may have a tendency to effectively cook in the presence of the heating and cooling cycles, forming a residue that can be seen on the wick  116  as a dark section. To the touch, this cooked residue is sticky, and may leave a mark on other surfaces used to touch the wick  116 . It should be noted that the precipitate is at least partially soluble in e-liquid, as at least some of the components of the residue are left behind from the vaporization of e-liquid. As e-liquid is drawn across the wick  116 , it is able to dissolve at least some of the residue components, helping to spread the residue across the wick  116 . This reduces the apparent concentration of the residue, but increases an overall perception of discoloration within the wick. 
     As the residue reaches the outer edges of wick  116 , the residue can be carried out of wick  116  and into e-liquid within wick feed lines  108 . While wick  116  is often made of materials such as cotton, linen, hemp, wool, nylon and other bulk materials, diffusion barrier  124  may be differently formed. In some embodiments diffusion barrier may be an engineered material that forms a semipermeable barrier allowing a one way path for e-liquid from the reservoir  102  to the wick feed lines  108  and wick  116 . It should be understood that in some embodiments it may not be possible or feasible to have a true one way path for e-liquid, and a directionally preferred path may be provided so that e-liquid can move through the barrier more freely in one direction (e.g. from the reservoir  102  to the feedlines  108 ) than the other. In other embodiments the diffusion barrier  124  may be formed of a nylon sponge that slows the movement of e-liquid between the reservoir  102  and the wick feed line  108  / wick  116 . In such an embodiment, nylon sponges  124   are placed within wick feed lines  108  so that they also optionally extend into reservoir  102 . E-liquid within reservoir  102  will saturate the nylon sponge  124  and migrate into wick feed lines  108 , helping to saturate the wick  116 . The characteristics of the nylon sponge diffusion barrier, including a saturation speed, can be defined through properties such as the density of the sponge. Residue that is drawn outwards through sponge  116  may be able to visually foul e-liquid within the feedlines  108 , but will be less likely to be able to migrate through diffusion barrier  124 . As the device is used, e-liquid from the feedlines  108  is drawn across the wick  116 , and e-liquid within nylon sponge  124  will drip into feed lines  108  through gravity, to aid in replenishing the e-liquid available to the wick  116 . Nylon sponges  124  will remain saturated with e-liquid as they are also in contact with the e-liquid within reservoir  102 . 
     It should be noted that a variety of different materials could be used for diffusion barrier  124  including cotton, nylon, wool, linen, hemp and other materials that may take the form of a sponge, or may be woven into sheets and then rolled up and inserted into the wick feed lines  108 . Other embodiments, which will be described in more detail below, may make use of materials that may be conventionally described as membranes. 
     Some pod designs make use of a so-called cartomizer matrix within reservoir  102  to hold an e-liquid. The wick is inserted into the cartomizer matrix to maximize the potential for the wick to absorb e-liquid. The cartomizer matrix is typically used so that a less viscous e-liquid can be used without increasing the likelihood of e-liquid leaking from the pod. This structure of using a cartomizer matrix to have a large interface area with the wick is used in the embodiment of  FIG.  5 A . Although pod  100  has a similar structure to that shown in  FIG.  4   , a cartomizer matrix based diffusion barrier  126  is used in place of diffusion barrier  124 . The cartomizer matrix based diffusion barrier  126  extends through wick feedline  108  and optionally extends into reservoir  102 . This allows the diffusion barrier  126  to absorb e-liquid from reservoir  102  and hold it within wick feedlines  108 . Much as with the previous embodiment, e-liquid consumed can be replaced by the wick  116  drawing e-liquid that is carried within or across the diffusion barrier  126 . As shown in  FIG.  5 B , the wick  116  is surrounded by a heater  118  which in the illustrated embodiment takes the shape of a coil. The diffusion barrier  126  is formed to allow insertion of the wick  116  into the matrix. In such embodiments it may be possible for the interface area to be increased through fanning of the end of wick  116  as it engages with diffusion barrier  126 . 
     While residue may be drawn across wick  116 , diffusion of e-liquid (or residue borne by e-liquid) across barrier  126  is relatively slow, thus preventing residue-bearing e-liquids free movement across diffusion barrier  126  and into the e-liquid within reservoir  102 . It should be noted that residue carried by e-liquid leaving the wick  116  may in some circumstances enter into diffusion barrier  126  where the residue may be left behind, with diffusion barrier  126  acting to some extent as a filter. By causing a slowed migration of the e-liquid into the reservoir  102 , diffusion barrier  126  reduces the likelihood of fouling the e-liquid within the reservoir  102 . 
     In  FIG.  6   , a similar pod structure to that illustrated in  FIGS.  4  and  5 A  is presented. A different diffusion barrier  128  is employed. Diffusion barrier  128  sits atop the end cap  106  and resilient cap  120 . This provides a similar form of protection to that shown in  FIG.  4   , but the diffusion barrier  128  can be formed differently, and in some situations, it may provide for a simpler manufacturing process. In some embodiments, diffusion barrier  128  may resemble a membrane that allows for different rates of diffusion in different directions. 
     Diffusion barrier  128  may be implemented as a barrier that allows the weight of e-liquid within reservoir  102  to push e-liquid through a one-way barrier  128 . It should be understood that in this embodiment, barrier  128  may be acting as a barrier to net total transport in the direction moving towards reservoir  102 . Thus diffusion barrier  128  may function like an expanded polytetrafluoroethylene (ePTFE) material such as Gore-Tex™ or another so-called durable liquid resistant barrier. In such an embodiment, barrier  128  is oriented so that the large pores are facing into the reservoir, and the smaller aperture pores face into the wick feed lines  108 . This allows for the migration of e-liquid into the feed line  108  so that e-liquid from reservoir  102  can replenish wick  116 , but e-liquid fouled with residue cannot as easily cross the barrier  128  and foul the e-liquid within reservoir  102 . When inverted, there is a much smaller amount of e-liquid atop barrier  128 , and the e-liquid is facing smaller sized pores to enter barrier  128 . This greatly reduces the risk of residue migrating through the barrier  128  in sufficient quantities to foul the e-liquid within the reservoir. 
       FIG.  7    illustrates a cross section of pod  140  that makes use of a vertically oriented wick  152 . Pod  140  has a reservoir  142  for storing e-liquid. Within pod  140  is a post wick airflow passage  144 . Upon being filled with e-liquid, end cap  146  can be inserted. The sealing mechanisms used by end cap  146  and reservoir  142  are not shown in  FIG.  7    as they are not germane to the current discussion of this figure. As with previous figures, electrical leads  148  connect to the heater  154  which is in engagement with wick  152 . A pre-wick airflow passage  150  aligns with both the interior of wick  152  and the post wick airflow passage. In operation, power is delivered across the electrical leads  148  and heater  154  will volatilize e-liquid drawn across wick  152 . Residue that may form is likely to form on the interior of the wick  152 , and it will migrate outwards across a narrow width of wick  152 . Where in prior art embodiments, the residue would then be in contact with the e-liquid stored within reservoir  142 , in the illustrated embodiments, a diffusion barrier  156  prevents or retards the movement of residue from the wick  152  into the reservoir  142 . In some embodiments, diffusion barrier  156  is a material similar to a cartomizer matrix, that is a sponge of nylon or concentrically wound layers of a wicking fabric such as cotton, linen, wool or other such material. 
     As before the speed with which e-liquid can migrate through the diffusion barrier  156  is either directionally based, or it is slowed by the diffusion barrier matrix. By at least slowing the movement of e-liquid from the wick back into the reservoir  142 , residue is prevented from entering the reservoir, preventing (or at least delaying) the visual fouling of the e-liquid. 
       FIGS.  8 A-C  present an alternate embodiment of the present invention, in which the characteristics of the diffusion barrier  124 ,  126  and  128  can be integrated within a wick  130 . A pod including such a wick could be used in a conventional pod that may or may not make use of a distinct diffusion barrier between the wick and the e-liquid within the reservoir. Wick  130  uses capillary action to draw e-liquid from the outer edges towards the middle of wick  130  where the e-liquid can be heated by heater  132 . Residue that may form from the heating process will form in the middle of wick  130 . However, unlike previously described wicks, wick  130  is designed with capillaries  134  that are shaped to encourage e-liquid to be drawn in from the outside edges of wick  130  towards the middle of wick  130 . This helps prevent the outwards migration of any residue formed during the heating process. 
       FIG.  8 B  illustrates a cross section of the wick  130 , surrounded by heater  132  at section line 8B. The wick  130  is formed to have capillary passages  134  that at this location within wick  130  are relatively large, and that effectively dominate the profile of the wick  130 .  FIG.  8 C  illustrates a cross section of the wick  130 , surrounded by heater  132  at section line 8C. The wick  130  has capillary passages  134  that are smaller than they were in  FIG.  8 B , resulting in a greater amount of wick  130  in the profile at this point. This reduction in the sizes of capillaries  134  can be achieved through a number of different techniques. In some embodiments, a wick  130  made of materials such as cotton, hemp, linen, wool, and synthetic fibers such as nylon, can be compressed (possibly using the winding of heater  132  to create the compression) so that the capillaries become compressed and smaller in the middle of the wick, and larger and less compressed near the edges. 
     In other embodiments wick  130  may be made of a material such as a ceramic in which the sizes of capillaries can be controlled in the manufacturing process. In some embodiments, the wick  130  may be formed of a resin or polymer coating on the heater  132 , with grooves on the surface (and possibly within) the resin or polymer to act as capillaries. In such wicks, the sizing and spacing of the capillaries can be engineered to allow for the capillary profiles discussed above. 
     In other embodiments, wick  130  may be made of materials such as glass fibers that can be manufactured with different profiles along their length. This would allow for the selection of fibers that are narrower in profile at at least one end than they are in the middle. This would create capillaries between the fibers that narrow from at least one of the ends towards the middle of the wick  130 . It should be noted that a similar structure may also be possible using a wick  130  made up of carbon fiber or other such materials. 
     As noted above, there are many different embodiments for a wick  130  depending on the choice of the material of manufacture. 
     It should be appreciated that in the above embodiments, the problem of residue migrating from near the heater, through the wick and back into the e-liquid within the reservoir are mitigated through the use of a diffusion barrier. This barrier is interposed between the wick and the reservoir, allowing for the barrier to resist the migration of residue into the e-liquid within the reservoir. The barrier slows or prevents migration of the residue in any of a number of different ways including preferentially permitting flow of e-liquid from the reservoir towards the wick, slowing the flow of e-liquid, filtering the residue from e-liquid during migration through the barrier. This allows for the migration of residue to be sufficiently slowed that during the course of the finite life of the pod, the residue is impeded from fouling e-liquid within the reservoir. In some embodiments this is done with a horizontal wick, while in others it is implemented with a vertical wick. This can be used for both nicotine bearing e-liquid as well as an atomizable liquid carrying cannabinoids. 
     It should also be understood that this arrangement using a diffusion barrier could be implemented in any of a non-refillable pod, a refillable pod, and a vaporizing system that has a reservoir integrated into the overall device having a battery and a control circuitry that may take the form or a processor, or even simply using a pressure sensor or switch to modulate power from the battery to the heater. 
     Although presented below in the context of use in an electronic nicotine delivery system such as an electronic cigarette (e-cig) or a vaporizer (vape) it should be understood that the scope of protection need not be limited to this space, and instead is delimited by the scope of the claims. Embodiments of the present invention are anticipated to be applicable in areas other than ENDS, including (but not limited to) other vaporizing applications. 
     In the instant description, and in the accompanying figures, reference to dimensions may be made. These dimensions are provided for the enablement of a single embodiment and should not be considered to be limiting or essential. The sizes and dimensions provided in the drawings are provided for exemplary purposes and should not be considered limiting of the scope of the invention, which is defined solely in the claims.